A G E N E T I C A N D C Y T O L O G I C A L A N A L Y S I S O F

O E N O T H E R A P R A T I N C O L A A N D O N E O F I T S R E V O L U T E - L E A V E D M U T A T I O N S 1

]~Y STERLING EMERSON

Win. G. Kerclchoff Labor)to'ties of the Biological Sciences, Califo,r,nia Institute oJ" ;f echnology

(With Four Text-figm~es)

CONTENTS

Ingrod ust ioa New appea.r~nee of mu~. formos~t. Description of Ocnolhsra prati.ncola E tg~)ica, and of rout. Jbrmosa Gene symbols [['he 2~ generations Cllromosomes of t,he ditierent, complexes Ciu'omosome configurations of hybr ids Identiflcat,ion of chromosomes Locat,ion of genes in t,he chromosomes The F 2 and back-cross generat ions Posit ions of t, he genes in the chromosomes Origin of mug. formosa from l~ratincola "Interst , i t iM segmen t s " The different revolute-leaved mutat , ions of Ocnothera ~rati'ncola "h'Iass ml~t,at,ion" S u m m a r y and conclusions R, eferenees Appendix

INTI%ODUCTION

PAGE 315 319 320 320 320 321 321 322 32,~ 324 327 327 331. 337 339 339 340 34-1

ON~ strain of Oenothera pratincola from Lexington, Kentucky (known as strain E) was found by Bartlett (1915) to throw varying percentages of revolute-Ieaved types. In some progenies these "mutat ions" made up all or nearly all of the viable individuals, but in such progenies there was an accompanying increase in non-viable seeds. This phenomenon Bartlett called "mass mutation". The revolute-leaved mutations were of four sorts :formosa, albicans, revol,uta and setacea. Front self-pollination

t A report, of exper iments conducted in part~ at~ I,he CMifornia Insgit,ute of Technology a n d in par t a t t,he ]3otanical Gardens of the Univers i ty of Michigan. I wish to ~ake Lhis oppor tun i ty go thank ProL H. It. Bar t le t t and ])r Frieda Cobb :Blanehard of the Univers i ty of ~'Iielfigan for some of the mater ia l utilised, for the facilities placed at, m y disposal and for their general hel l) m~d criticism.

St rMn C typica St rMn E typica

316 A Genetic and Cytological Ancdy,~is of O. p r a t i n c o l a

these nmtations yielded only revotnte-leaved offspring. The same was tn:ue when the mutations were pollinated by the fl~bleaved parental form (typica), ]~ut when the parent form was pollinated by {~he mutant forms the progenies were flat legved except for g nmnber of revolute plants corresponding ~o the number and types produced from self- pollination of the parent form. These data showed that the flableaved parent form and the revohte-leaved mutations hgd similar pollen com- plexes (called the fi complex) but differed in their egg complexes (the

complexes). One of the rcvolute mutations of strain E (mut. jbr,mosa,) has been

studied intensively by Dr Fried~ Cobb Blanchard (Cobb and ]~artlett,, 1919; Cobb, 1921; Blanohard, 1929). I:[er observations and interpreta- tion (Bla,nchard, 1.929) may be smmnarised as follows:

Strains C and E ofpratincola have identical egg complexes (~.) carrying a dominant gene (F) for flat leaves. The pollen complexes (fl) of strains C and E differ by a single gene, F being carried in the fl of C while the /3 of strMn E carries the recessive f (revolute ]eaves). The f/d complex of strain E occasionally functions in eggs, giving rise to the homozygous form ffi.ffi known as mug. setacea. Dr Blanchard interprets the occur- rences of rout. formosa in the progeny of ]3 typica as resNting from an interchange of whole chromosomes between the two complexes (called "whole chromosome crossing-over") by which one of the chromosomes of ~. has been replaced by ghe chromosome of fi which carries the gene L The new c~. complex carrying the f chromosome of fi in place of one of the original ~ chromosomes is designated f~'.

The different forms of Tratincola ~ogether with their constitutions and breeding behaviour may be smnnaarised in tabMar form:

..; F~.?Pfl ... f lag-leaved, t r u e b reed ing .

... F~..ffl ... f lag-leaved, " m u t a t , i n g " to for,mesa,, albicans, rcvohtla a n d 8elacca.

mug. sdacea, (E) ... ~/d .ffl ... r evo lu te , grue b reed ing . nlui~.Jbrmosa (E) ... f~' .~fi .,. revolul,e, b reeds Lrue for r evc2a te but; ~ 'mul ;a tes ' '

~,o o the r forms i n c l u d h l g mug. seh~cea. ... F~,.I/J ... f l ab lc~vcd , e q m v M e n t go E lypica. ... i~.'.f/d ... r evo lu te , e q a i v M e n t go mug. jbrmosa,. ... ~ . f f l ... f l a tdeavcd , e q u i v a l e n t go E typica. ... f ¢ ' . F f i ... f l ab l eaved , seg rega tes in F~ i n t o :

1 fa.' Aft, revoluf~e, l i ke toni). Jbrmosa; f f~.' . F f l ' / t i l t - l e a v e d , i n d i s t i n g u i s h a b l e f rom

2 \ F ~ , . f f i f t h e F i ; l F a ' . F f l , f l a b t e a v e d , grue breeding.

Dr Blanehard's interpretation is based on the assumption tha~ t~he chromosomes of the t~wo complexes, c,. and fl, are not homologous. However, since the establishmen~ of ]3elling's hypothesis of chromosome

E l, ypica x formosa formosa x E @pica C typica x for,mesa jbrmosa x C typica

~TEI%LING ]~]ME]gSON 317

r ing formMfion in Oenothera b y t rans loca t ion (Darlinggon, 1929, 1931; Cleland and ]31akeslee, 1930, 1931; Emerson and S tu r t evan t , 1931, 1.932; Rennet , 1933; etc.), we know t h a t the two complexes m u s t be made up of homologous elements which, however , are differently a r ranged in the chromosomes of the two complexes. I f one complete ch romosome of z, should be replaced by one of ~he chromosomes (the f -car ry ing chromo- some) of fl, the result ing fz.' complex mus t ca r ry a dupl ica t ion of one ch romosome segment and a t the same t ime be deficient for another ch romosome segment as i l lustrated in ~he accompany ing d iag ram (Fig. 1). While dupl icat ions are often viable as gametes in plants , i t has been found t h a t gametes deficient for a pa r t of a chromosome ordinar i ly do no~ func t ion unless the region involved is small (a discussion of m a n y such cases together with an except ional instance is to be found in a paper by Sgadler, 1933). Hence, a l)rio~'i, i t is no t reasonable go suppose t h a t "who le ch romosome cross ing-over" as pos tula ted by B lancha rd would resul t in viM)le gametes unless something fur ther happened to com- pensa te the deficiency. 1

Since genes lying in ring chromosomes of Oenothera m a y cross-over f rom one complex to the other w i thou t al tering the ch romosome con- f igurat ion (Emerson, 1931 a; E m e r s o n and Sturgevant , 1931, pp. 615-16; l%enner, 1933) as i l lustrated in the accompany ing d iagram (Fig. 2), i~ was concluded (Emerson and S tu r t evan t , 1931) t h a t " t h e jbrmosa of pratincola is p robab ly also to be referred back to a c ross-over" . There is one genetic result which inval idates this interpretal~ion. The cross ty2)ica ~{ xJbrmosa (Cobb, 1921, Table 29) segregated in/~'2 in to 3 flat : 1 revolute . Typica hi_ is a h o m o z y g o u s flat- leaved segregate f rom the cross formosa x C tyl)ica which on Dr Blanchard ' s scheme is designated Fz. ' . Pfl. I n this hybr id the egg complex (~.) came originally fromJbrmosa,

While the eytologicM findings of Kulkarni (1929) also are apparently not in accord with this interpretation, the mageriM go be reported in this paper shows that his materiM was not critical. I-le observed a ring of tburteen chromosomes in both l~rati'~cola E tyl)ica and in rout. ,for'~tosa, whereas if the ~.' complex ofjbrmosa has one chromosome in common with f/3, rout. jbr.mosa should have one chromosome pair. Kowever, Kulkarni's obserw~- t:ions were made on au inbred line many generations removed from the plants utilised in the genetic experiments, anti furthermore, recent a~tempts to repeat the earlier genetic tlndings with this strMn have failed to yield the Mendelian segregation characteristic of the earlier experiments (J31anehard, unpublished). As will be shown below, the new formosas appearing in my cultures do have one chromosome pair. It is probable that the configural;ion of chromosomes in the strain used by ](ulkarni has changed at stone time subsequent to the earlier genetic experiments (compare with the altered chromosome configuration in "francis('~o~a s~dfwrea"--Emerson, 1931 c~). ](ulkarni's observation on platlts of strain 1~![ (descended from the cross formosa, x C ly2)ica) is in agreement with Dr ]31anehard's in~erpretal.ion; the gene pair ~F/~ must be in the pMring.ellronlosome.

318 A Genetic and Cytolocjica~ Anagysis of O. prathacola

but has lost the gene ~ and rega.ined ~he gene ~P from the fl complex of strain C by ordinary Mendelian recombination. I-Iad the el. complex of formosa arisen by crossing-over as described above it shoNd s~ill have the chromosome make-up of the ~ complex of i)ratincola, E tyl)ica. To bring about the segregation in crosses with the fi complex of (J ty2)ica, the chromosomes carrying ~ or F in the p of C typica, the c/. of]brmosa (and consequently in the ~ of E typica) must be identical with respect

~. a-b c-d e-f g-h i - j k-I m-n

n-a b-c d-e f -g h-i j-k I-m :p Fig. 1. Schematic representat ion of the chronmsomes making up ~he ~. ~nd fl complexes

of Oe. ~)rati~zcola E l!/pica. The segments Ie~ered a to n represen~ homologous regions which are arranged differently in the two complexes. I f any ~ eln'omosomc such as a . b is replaced by one of l)he fl chromosomes with wlfich it~ is pa%iMly homologous, such as b , c , l;hc resul t ing z.' complex will carry one segmen t (c) in duplicate bug will entirely lack another s e g m e n t (a in this instance).

J L q :r

A,

J L

B Fig. 2. The pairing relations in a ring of four arc illusgrgged iff A. I f a cross-over takes

place in the region indicated by the arrow, the gone ~ will be gransferred from ctn'omo- some 1 .6 of [3 go chromosome 3 . 6 of z. wil~houg altering l)he chromosome configuratfion in ~,.fl hybrids, Tha t is, abe a complex sgill has ct~'omosmnes 1 .2 and 3 .4 and the fl s~ill has 1 .4 ~md 2.3 as indica ted iu ]K

to their end homologies. The z. complex in this hybrid, coming from E tyl)ica through formosa, has supposedly remMned unaltered except that ~he gene F has been replaced first by f and then again by P; and when brossed to the fi of,/brvzosc~ the resulting hybrid should stilt ha, re a ring of fourteen chromosomes and give no segrega~iml for revolnte leaves. This is contrary to observation. From Dr Blanchard's interpre- tation, however, the ~' complex of/brmosa has a chromosome in common with the fi complexes of both strMns. The recovered M tyl)'ice~ should

STE~ALING EMEIgSON 319

still have this chromosome, and when pollinated by t h e fi o f f o rmosa should yield a segregating F 2 progeny, as was aetnally observed.

Thus i~ can be seen ~hat none of the interpretat ions outlined above is enbirely free f rom objections. I-Iowever, a new occurrence of mut~.

Jbrmosa ham given ~he oppor tuni ty of studying its origin by a differen~ method. This method u~ilises hybrids with other species and[ forms of known genetic and cytological behaviour. The genetics of some of theme species ham been worked ou~ in detail by I~enner. Those are--Co. La- ,marcl~iana, : v d a n s .gaudens ; Oe. suavcolens : albiccc, ns ~. . f lavens ; Oe. Hoolceri : homozygous "Hoolce,ri ; Oe. f r a n c i s c a n a : homozygous hfranc i scana ; and Oc. cldca, g inens i s : excellens .punetu~ctns. The forln called N is a 'nandla, ,rub)'icalyx, old-gold, the pollen complex of which is designated Nd. Identifications of the chromosomes making up the various complexes have been made by Cleland and Blakeslee and by Emerson and Stur tevant .

N~w A~Ea~ANCE O:~ ~'EUT. ~On;~O~'A

In a culture of fifteen plants f rom self-pollinated Oe. pra t incola E typ ica (obtained from Prof. Bar t l e t t and Dr ]31anchard) grown in 1931 t, here were two revolute-leaved plants. One of these (No. 22~i3-8) was a vigorous and fully fertile plan~ which was found upon cytological examination to have a ring of twelve chromosomes and a pair. Flag- leaved sibs of this plant were examined and found go have a ring of fourteen chromosomes, as had been reported by Kulkarn i (1929) for E typica . In this instance, then, the appearance of the r evohge character was accompanied by an al terat ion in the chromosome configuration. ~ Progeny of this revolute-leaved p lant (from self-pollination) were grown the following summer at the Univers i ty of Michigan and were identified by Prof. Bar t le t t as mug.,/b,rmosa. The fiat-leaved pa.rent (No. 2058-9) of this new mat . ,/br,m.osa ha,d been crossed with the s tandard " t e s t e r " stocks, and the new mug. f o r m o s a (the original plant, No. 22~I3-8) was crossed go the same forms.

t 'rite egg complexes of Oc. attc~veolc~.s ~nd of Oc. bicn~ia have been e~lled (dbica~s by I%enner. E~rlier in this l)~per ~ revoluge-lcaved mugat,ion of Oc. 'pratincola. has been re- ferred go wttieh Bartlegg (i915) n~med mug. albica, ns. k[ereafter in this paper the germ alblcans wilt be used go design~e the complex albicans. Since there will be Ill)ale reference go mug. cdbica.ns il~ is hoped that no confusion will ensue.

" A second ~ppearance of mug. form.osc~ was observed in the 1934 culture of E typica. This pl~nb similarly h~d ~ ring of twelve cln'omosomes and one pair.

320 A Genet ic a n d Uytolocjical A n a l y s i s o f O. p r a d n e o l a

])ESOI~,IPT1ON OF OENOTH_ER=! PR~qTINOOLA ]~ TI'PIC'A

aND OF ~UT. FOml~O,S'A Oe. pratincola and. rout. Jb'rmosc~ have been described and figured by

Bardett (].915). Ill the present connection there are but l~wo characters aside fl'om the revolute character itself which need special notice. Both t?/picct and formosa have leaves with red mid-ribs, sometimes called red nerved. Both ibrms have red[ pigmenta, l;ion in die papillate bases of tile long simple hairs on the seems and ovaries (the character known as "puncture") with t]ae accompanying red pigmenl;adon on the bud cones which, however, is relatively Nint especially on the buds of tyl)ioa.

GENE SYMBOLS

l~ecessive gene for re volute leaves. P Puncture stems and ovaries, dominant to non-puncture (p). ps Puncture wid~ "s tr iped" bud cones, allelomorphie to P and p with

the bud colom' incompletely dominant. pr Puncture with ",rubricalyz" pigmentation of bud cones and hy-

panthia, the rubrica, lyx pigmentation incompletely dominant to other members of the allelomorphic series.

s Sulphur flower colour, recessive to deep yellow. v "vetaurea", old-gold flower colour, recessive to normal yellow. n nanella, an extreme dwarf, recessive to normal. d Dwarf stature, less extreme than nanella, veining of leaves irregular,

recessive to normal. R l~ed nerved, dominant. ]3 Broad leaves dominant.

THE F 1 GENEIgATIOIgS All funetimling pollen of Oe. l)ratincolct E typica and of rout. formosa

carries the fl complex. The genes carried by fl can be determined from appropriate crosses using y)ratincok~ as the pollen parent. Tlle experi- lnents of Bartlett, (].91.5) and of Blanehard (1929) show that fl carries revolute leaves (f).

The hybrids (Hoo~:er~ x pratincola) F 1 hHoolcer,;, fi have white nerves, flat mid-rib hairs, flag leaves and the punctation of Hoolce~'i. The hybrids (suaveolens x l)ratincola ) F:t albicans.fi and f lavens.fi have white nerves, flag mid-rib hairs, flag leaves and the pnnctation of 2)rati,ncola--l;he albica,ns andflavens twins are distinguished by leaf shape. These hybrids and others of similar import show that in addition to ~, t)he fi complex carries a rather weak allelomorph of ps and the recessive allelomorph (r ?) of the gene for red nerves. _Plavens and albic¢tns both carry r and p.

STt~I~LIN¢4 EM~ICSOh~ 321

The hybrid s'(p'ratincoh~ x sttaveolens) F~ ~ .Jlavcns have red nerves, erect mid-rib hairs, flat leaves and no punetation. These hybrids and others not record ed here strew th at the ~ complex of pra, tineola carries the dominant gene for red nerves (R?) and recessive p. In addition, c~ and fi can be distinguished by the character of the hairs on the under-surface of the mid-ribs (see Fig. 4-, ]?. 338). Outcrosses using p,ratiqzcola, as the female parent produced a total of seventy-nine ~ and six/3 twins, indicating that 90 per cent. or more of the :Nnctioning eggs carry the ~ complex.

The hybrids [nmt../b,rmosa × (sulfu~'cns. s flavcns)] ]71 f~'. s Jlavens had red nerves and fine punctation. Therefore in addition to the f from/3, f~' carries ps from /3 and l:l from ~ of p,ratiqwola. In the various out- crosses of this sort there were forty-seven f~' twins to eight/3, indicating tha t about 85 per cent. of the functioning eggs carry the re/complex.

Sum'ma~'y. P,rati~wolct ~ carries the genes lt, p, :F ; pratincola/3 carries the genes r, ps, f; andfo,rmosa f~' carries the'genes R, ps, f.

(AFT~ Eh~E~SON ~hZD STmVi'~VX~T, 1931) ~l]ookeri 1 . 2 , 3 . 4 , 5 . 6 , 7 . 8 , 9.10, 11.12, 13.14. ~ franci~cr~:na s ' 4 }~francisca't~.a r 1.2, 3.4., 5.6, 7.10, 8.9, i1.12, 13.I4 cxccllcns J f~ave,~s \ 5. " s f l a v e n s f 1.4-, 2.3, 6, 7.8, 9.10, 11.12, i3.14. Nd' 1 . 2 , 3 . 4 - , 5 . 6 , 7 . 1 4 , 8 . 1 3 , 9.10, 11.12 velans 1 .2 ,3 .4 - ,5 .8 ,6 .7 , 9.10, 11.12, 13.14- albicans 1.4. and either 7.10 and 8.13 or 7.14- and 8.9

CIII~OiVfOSO~E CONFIGUI~ATIONS OF I:IY]3I~,IDS

In the following list of chromosome configurations, the numbers separated by commas indicate the number of chromosomes in each group. For example, "4-, 4, 2, 2, 2" indicates two rings of four chromo- somes each and three pairs, and "12, 2" represents a ring of twelve chromosomes and one pair, etc.

~. hj'ranciscanc~ 4, 2, 2, 2, 2, 2 (3 plants) ~. hHoolceri 4., 4, 2, 2, 2 (2 plants) ~..flavens 4, 4, 4, 2 (3 plants) v..Nc~ 8, 2, 2, 2 (2 plants) c~.vela~.s 8, 2, 2, 2 (1 plan~) ~,.fl 14. (2 1)langs; also :Kulkarni, 1929) c,~:cellens.fl 12, 2 (1 plant) ~Hookeri.fl ] 0, 2, 2 (:3 plants)

Jlave~s.fl 8, 2, 2, 2 (4 I)lants) f~'.fl 12, 2 (1 plant) f~.'. s d ~lfra,~ci~ca~a, 4., 4, 2, 2, 2 (several plants) fez'. hllookerl: 4, 4, 4, 2 (several plants) f~' . s flavc~l.s ,l, 4, 2, 2, 2 (several plants) fa.'.Nd' 8, 4, 2 (l plant) ~ ' . vda .ns 8, ~J, 2 (l plant)

322 A Genetic and Cytologiccd Analysi~s of O. prg t inco l~

IDENTII~ICATION OF CHI~OMOSOMES

If one grants Belling's assumption that adjacent ring chromosomes are homologous throughout the regions neighbouring the end-to-end attachments, it is possible to work out the corresponding homologies of the end-segments in chromosomes of different complexes from the con- figurations observed in the hybrids (Cleland and Blakeslee, 1930, 1931; Emerson and Sturtevant, 1931, 1932; l~enner, 1933). From the hybrid configurations listed above it is possible to identify most of the chromo- seines in the complexes of Oe. p~'ati,~cola and rout. jb~',m, osa.

The ~. complex of pra, ti~wol(~, has five pairs of chromosomes in hybrids with l~?'a~c,isca~a, which means that z. has five chronmsomes of more or less identical homologies with five of hfl'a~ciscana,. With .flave~s, the

complex has but a single pair. Since z. has four more pairs with ~?'a,~zcisca, na than with flavens, ~ must have four chromosomes with end-homologies identical to four ~'~'anciscana chromosomes but not iden- tical to anyflave~zs chronmsomes. There are only four such chromosomes in ~f~'a,~ciscana, 1.2, 3.4., 7.10 and 8.9; and these must consequently be present in ~ and constitute four of the five chromosome pairs in c,..~f~'a, nciscana. In ~.flave'r~s, these four chromosomes will form two of the rings of four chromosomes together with 1.4 and 2.3 and with 7.8 and 9.10 of flave~,s. The pair in c,...flctve~zs and the fifth pair in oz. ~fra~,- ciscana must be one of 5.6, 11.12, I3.14,

In z.. Nd, chromosomes 7.10 and 8.9 of z. will be associated in the ring of eight chromosomes with 7.14-, 8.13, 9.10 and one other (5.6 or 11.12) of Nd~. Chromosomes 1.2 and 3.4. will constitute two of the chromosome pairs and the third pair nmst be either 5.6 or 11.12. Since both these chromosomes are present in hfl'anciscc~na and in flavens, the remaining pair in ~.hf~'a~wisca~a, and in ~..flavens must also be either 5.6 or 11.12, thus eliminating 13.14. as a possible pair in these two hybrids, since there is only one pair in z../lave,J~,s and only five pairs in ~ . ~ f ~'a nsisca na,.

In cz.vdans, chromosomes 7.10 and 8.9 of ~ will be associated in the ring of eight ?~ith chromosomes 5.8, 6.7, 9.10 a,nd one other (11.12 or 13.14-) of selans. Two of the three pairs will again be chromosomes 1.2 and 3.4-, leaving either 11.12 or 13.14- to constitute the remaining pair. Both chromosomes 11.12 and 13.14- are also present in.fla, vens and in 1~f~'anciscana, and one of these must consequently be the remaining pair in hybrids between ¢ and these two complexes. I:[owever, it has been shown in the preceding paragraph that 13.14- cannot be the pair

STER, LING E~IEI~SON 323

in either of these hybrids. I t follows then that chromosome 11.12 must be the pair in ~.flavens, the third pair in ~. N~ and in g.'vel, a'Jbs, and ~he fifth pair ill ~.hfrancisca,nct. To form the ring of Ibm: in ~.J~fr~,,nciscana and I~he third ring of four in cz :fla, vcns, and to compleLe the rings of eight in ~.N(? and in z..vela,ns, ~ must have two chromosomes representing an interchange of ends bel, ween chromosomes 5.6 and 13.1~k That: is,

must have either 5.14- and 6.13 or 5.13 an([ 6.1,l. F rom the informa- tion available it is impossible to determine which of these alternatives is correct. We may therefore write:

c~: 1.2, 3.~1, 7.10, 8.9, 11.12, and either 5.1~L, 6.13 or 5.13, 6.1,1-.

The fl complex of '2)'rati'ncola has three chromosomes in common with .flave,ns and none wi~h ~, and must therefore have ~hree of tile six chromo- seines by whiehfiavc,ns differs from q_ Furthermore, since there is no ring of four chromosomes in ~.fl, fi cannot have both I .4: and 2.3, nor both 5.6 and 13.14, nor both 7.8 and 9.10. Since these are the six chromosomes by which.flavens differs from ~, it is evident tha t fi must have one member of each of the three sets listed above. The pair in cxcdl, c%s.fl and one of the pairs in l~Hoolccr'i.fi must be either 5.6 or 13.1~1, and ~he second pair in hHoolcc,ri.fi lnt[st be either 7 .8 or 9.].0. This is as far as the identification of the chromosomes in the fi complex can be carried from the cytological data available. By ~he use of genetic data however (see below), the identification can be advanced somewhat.

fi: either ] .4 or 2.3, either 5.6 or 13.1~1, and either 7.8 or 9.10.

The f~' complex of formosa has three pairs with s d l~ranciscana an([ a single pair with nHoolce~'i, and must therefore have chromosomes 7.10 and 8.9 by which l~fra'nciscana differs from hHooZ:e,ri. The Is,.' complex also has three ]?airs withflavens and consequently nmst have chromo- seines 1. ~f and 2.3, by ~<hichflave,~s differs from hHoo~:e'ri. The remaining pair in each of these three hybrids must be one of 5.6, 11.12, 13.14. The pair in fc~.' .Nd must be either 5.6 or 11.12, and the pair in fc,.' .velans must be either 11.12 or 1.3.14. Whichever chromosome is [he pair in either of the last two hybrids must also be a pair in the first three hybrids. Hence, the remaining pair in all five hybrids must be chromo- some 11.12 for the same reasons used in the argument :['or the c,. complex. The remaining chromosomes must again be either 5.1,t and 6.13 or 5.13 and 6.1,t.

is,.': I.,1, 2.;], 7.10, 8.9, 11.12, and eittter 5.14:, 6.13 or 5.13, 6.1,1.

The fW complex offo,rmosa differs from tile c,~ complex of ln'atincolc~ J o u r n . of Genetics xxx~I 21

324~ A Genetic, and Cytological A'naly,~'i~" of O. p ra , t inoo]a

from which it is descended by bwo chromosomes, 1.~1 and 2.3. One of these was present in the fi complex of prati'ncola (chromosome 1.4-, see below) and may have come into f~' by "whole chromosome crossing- over", bug the other represents a :new combination of chromosome ends and must have arisen by some process cclnivalent t~o t~ranslooation. As noted earlier, if chromosome 1 .~t of fi ha:l simply replaced one chromo- some of z. (say 1.?~), I;he resulting complex would be a duplication for one chromosome end (4) and a. deficiency for ~motl{er (2). As it happens, hogh 1.2 and 3.(~ of z~ have bee~ replaced by 1,4: and 2.3, and all chromosome ends have been rel:ained in I)he haploid condifJon in the resull~ing complex.

LOCATION OF GENES IN THE CHgOh{OSOMES

(Am'~ EMerSoN a~D S'ruBT~VAN% 1932)

R in chromosome I . 2 of vela,ns (and of p'rati.ncola z.?). v in chromosome 1.2 of N~. ps in chromosome 3. ~ o~' s d J'/:ranciscct,~,a. pr ill. chromosome 3.4 of Nd ~. p in chromosome 2.3 offlavens and s.fla, vens. n in chromosome 3.4~ of Ndt s in chromosome 3.4 of s d ~:raneisca,na. s in chromosome 2.3 of sflave~;,s.

.flavens zygotic lethal in chromosome 5.6 offlavens. B in chromosome 7.8 of flavens and of s flave,ns (l:~enner and[

Cleland, 1933). d in chromosome 13.14 of s 4 l~rauciscana.

THE ~2 AND BACK-CROSS GENEI~ATIONS 1

The _F 2 generation from hybrid s flavens.fi helps to determine the constitution of the /? complex, As noted above, one of the pairs in this hybrid is either chromosome 1 .~l or 2.3, with s known to be carried in chromosome 2.3 of flave,ns. Hence s will be inherited with (i.e. lbfl~ed to) chromosomes in the r~ng of eight if the pair is 1 .~1-, but if the pair is 2.3, s will be inherited independently. The second pair in t~his hybrid is either 7.8 or 9.10 with 13 carried in chromosome 7.8 of flea,erie. I f the pair is 7.8, 13 should be inherited independently, if not it should be asso- ciated with the ring of eight. The third pair is either 5.6 or 13.14- with theflave'ns zygotic lethal carried in chromosome 5.6. Then if 5.6 is the pair, homozygons .flave~,s.]lavens, called ~utesce'ns, should appear as a

t AdditionM corolh~ry d~t,a are prescribed in ~,he ~ppendix a5 t~hc end of the proper.

~:1' EI :~LIN(: I _]~N E I ~ S O N 325

segregaag, while it" the pair is 13. ]4- no tutt;sce.~,s should ~ppe~r. This cross should further show whether f of fl is in one of the pairing chromo- seines or no[. The observed l?,, data were (cultures 2577 and 2578 of 1933):

I~B (J/avcm~'.fl) 372 F t~ (./lavcns. fl) 362

f B \ (/lavc,~.~ 41) 198 ~1) f , 17.13 ~nd F b (fl.fl) 19 f t3 ~nd f 1) (/9./~) :),

953

All plants had yellow flowers (S) and punebate stems (ps), and none was lul, esce,,,s (i,.c. Jh~vens.Jlavens). This means that s and p (in chromo- some 2.3) of fiavcns were associated with bheJlavcns lethal (chromosome 5.6) in (~he ring of eight~ in the hybrid, while B (in chromosome 7.8) ~md f segregated independently. Hence fi must have chromosomes 1.4, 7.8 and 13.114 in common witch ,flovens ~md f must be in either 1 .,t: or 13.14- of fi with the earlier data of Blanohard indicating 1 . t as the more likely, since 1.4 is the pair in ic~'.fi.

In the F,, from albicans.fi and in the back-cross to /? pollen the following data were obtained (Fe cultures 2471 and 2472, back-cross culture 2473 of 1933):

1P2 .~gok-oro88 F (albicans.fl) 247 86 i (albicans.fl) 120 72

434 229

M1 plants were punetate (ps) and had yellow flowers (S). These data show tha t revolute leaves (f) segregates independently of the rest of albicans ~nd ft. Chromosome 1.4 is known to be a pair in this hybrid and 13.1,~ of fi is kn.own to be in the ring, since cdbicans has either 8.13 or 7.14. Therefore f is in chromosome 1 .~l of fi:

fl: 1.4, 7.8, 13.14 with f in 1.4.

An ~ from hybrid f~'. s d. h fl'anciscc~na (cultures 2584, 2585 and 2586 of 1933) gave the following results:

310 * D 137 f4 71

518

The flat-leaved plants were discarded in the seedling stage and only the revolutes (f) were grown to maturity. These all had yellow flowers and red. nerves. In this hybrid, chromosomes I .~t and 2.3 o[' fzf are in a

21-2

326 A Genet ic a n d Cytologiccd Anaty~sis o f O. p r a t i n c o l g

ring of four with 1.2 and 3.4 of s d l~?'c~ncissc~na. The gene f is carried in 1.4 and s in chromosome 3.6. Plants homozygous for f from this cross must ordinarily be homozygous for chromosomes 1.,t and 2 . 3 , hence none of these would be expected to show ~he stflphur character (s) from thefl'andsca, nct parent. Since none of the revolute segregants had white nerves, R must also be in the ring of foul', tha t is in either 1.6 or 2.3 of f~'.

In nlugation ]b'r,m, osc~ (f~'.fl) with the configuration a ring of twelve and a pair, the pair is known to be 1.4 and{ to carry the gene f. Out- crosses show that R is always carried by the fc~/complex and never by/?. R must consequently be in the ring of twelve chromosomes and not in 1.6. Then, since R is known to be in either 1.4 or 2.3, it can now be definitely located in 2.3.

Since f is carried in chromosome ] .,l: of f~' and R in 2.3, the two genes should segregate independently in hybrid fz/.fla, ve'~.s in which 1.4 and 2.3 are pairing chromosomes. An Fo from hybrid f~..s flts'vens (cN- lures 2582 and 2583 of 1.933) consisted of 379 flat-leaved plants (F) and[ 51 revolute (f). There was segregation between heterozygous ps /p and homozygous ps/ps, but no recessive p /p plants appeared. There was an apparent segregation for intensity of the red-nerve character, perhaps R /R and R/r , but no white-nerved plants appeared. There were likewise no plants with sulphur flowers (s). For some unaccountable reason the recessive genes carried in chromosome 2.3 of,flave~zs (p, s and r) failed to appear in the F 2. The /~1 f~' .s.flavens was grown again and back- crossed to s lutescc~s. In the back-cross (f~'. s f lavcns)x s ,/lct, ve~zs (cul- tures 268,f, 2685 and 2686 of 193~t) there were 165 plants carrying R, pc, S, and th i r ty plants homozygous for r, p and s. Many plants were self-pollinated and seedlings were grown to determine which carried the recessive f. The results were:

R P S F S / r p F s 16 R P S f S / r i o F s 12 r p F s / r p F s 9 r p f s /rpFs 5

6~

Exact ly one-half of these cultures represent recombinations between F/f and the remaining genes. These data show tha t in a hybrid in which chrothosomes 1.6 and 2.3 are pairing chromosomes, the genes R, ps and[ s are very closely linked to each other but independent of ~. Conse- quently the genes R, ps and S must be carried ill chromosome 2.3 of f~'.

S T E I R , L [ N G ]~lVI~EI~,S O N 327

POSITIONS OF 'I?I-[E GENES IN TKE (JHROg'IOSO~KES

The genes P a.nd s (or their allelomorphs) are known to be carried in chromosome 3. ~ of such forms as ,velans, hHoolceri, ~ranciscana, etc., and in chromosome 2.3 of .fla,ve,~'~s and re.' leading to the conclusion' (Emerson and Stnrtevant, 1931, 1932; t~,enner, 1933) tha t both these genes are carried in the 3-end of both 2.3 and 3.4-. Y~enner (1933) has shown tha t n (e~rried in 3.4. of 'vcIans, N~, etc.) must lie in arm 4.. This conclusion follows from the observation that P and n can both cross-over from one complex to another independently of each other in hybrids in which 3.4. is known to be in a large ring (P independently of n in ,velans .rubens and in ,vclans .gaude.ns; n independently of P in the same two complex-heterozygotes and in n velans.albicans). This can only happen when two genes lie in different chromosome arms (see Emerson, 11931. a), and[ since P is in arm 3, n nlust; be in arm 4-. By a similar method I~enner has been able to show that the position of s in arm 3 must be distal to tha t of P, giving the order 3 s P . n 4. for this chromo- sonle.

The R of l)ratincola h as not been identified[ with the t~ of Lctma,rclciana, but the evidence indicates tha~ it is very likely the same gene or an alletomorph. Chromosome 2.3 of ~. ' carries ps from /1 in ann 3 and R front z., which therefore must be in arm 2, and must have been in arm 2 of chromosome 1.2 in the ~ of p,ratincola since chromosome 2.3 of re.' has arisen in part from ~ and in part from ft.

The gene for revolute leaves studied by Shull (1923) in Oe. La- ,marclciana was linked to the genes in the ring chromosomes (including chromosome 3.4.) and consequently independent of chromosome 1.2 wlnch is a pair in tha t species. The gene for revolute leaves in Oe. l)ra - tincola is carried in chromosome 1.4.. I t is probable tha t the same gene is involved in both cases and tha t i is to be located in chromosome end 4-.

OI~IGIN OF MUT. F O R O f O S A .[PgOSi P R A ~ I ' I N C O L A

I t has been shown above tha t the egg colnplex of mut../br,m, osa (re.') differs from the egg complex (z.) of Oe. p,ratincola E ty~)ica by two chromo- somes and by two genes. Chromosomes 1.2 and 3.4. of ~ have been replaced by chromosomes 1.4.- and 2.3. Of these, chromosome 1.4. carrying the gene f has come directly from the pollen complex (/~) of tyl)icc~, but chromosome 2.3 is a " n e w " chromosome made up of the 2-end of chromosome ] .2 from z~ a, nd the 3-end of chromosome 3 .x of ~. This new chromosome carries genes fl'om both parental complexes,

328 A ge~el, ic a~d Cytological A ~ c @ s i s of O. p r a t i n e o l a

R from 1.2 of ~. and ps t¥om 3.x of ft. The studies of Bartlett and of Blanchard indicated that the fi complex of naut. ]br'mosc~ was identical with that in the pareneal form, t7/1)7c~,, and this conchsion is supporl:ed by the observed behaviour in my own crosses.

~£hese changes accompanying the appearance of mat. fo,r,mosa, re- semble closely the changes accompanying the appearance of the so- called half-mutations in Oe..Lc~'ma~'cbic~'~t. In the half-mutants, one Lc~.mct'rclcict~z~ complex has remained unaltered while the other complex has been changed go include certain chromosomes normally present in the unaltered complex. Darling~on (1929) and Cleland and Blakestee (1931) have shown lmw these half-nmgants can arise from translocations between one chronmsome of one complex (velct~s) and one chromosome of the other complex (ga,~,tde'~ts). Mutation Jb~"m,o~'a, migllt similarly be the result of a reciprocal transloeation between chromosome 1.2 of ~. and 3.x of fi in iJrati~colct.

Mutation jb~'mosa differs slightly from the half-mutants of Oc. Lc~- ')~~'clcia~za with respect go the lethal situation and to the frequency of occurrence. In the half-mutants of Laq~za'rclcic~,a, the modified complexes have los t the lethals characteristic of the parental complex and are entirely lethal-free, whereas the re.' complex of rout. fo~',mosr~ retains the pollen lethal characteristic of the ~. complex of p.ra, ti,~zcolc~. Tl~e most iYequent half-mutant from La,,m,a~'cl~:ic~,~.c~ is apparently mue. ,r.~b~'i,~.e~'v,~s, for which de Vries (1919) reports the rsgula, r occurrence of one per ~housand from inbred Lco~.c~'cl&~c~. From inbred[ 1)~'c~ti~,col.a, Bar t le t t (1915) found approximately thirteen formosas per thousand, a, nd the recent cultures growl~ by Blanchard and Bartlett (not published) and by myself show about the same rate of production of ~his form.

~_['he relatively high frequency of appearance of rout. fo,r,m, osa suggests that the new chromosome arises by some sne]~ regular process as crossing- over. This could be accomplished if there was ,% region (the so-called "interstitial" region of Darlington, 1931, 1932; Sansome, 1932, 1.933) near the middle of chromosome 1.2 of ~ which is homologous to a region near the middle of chromosome 3 .x of fi, provided that this region is so oriented that crossing-over will result in the association of end 2 with end 3 in the "5~ew" ehromatid. Such a scheme is ilhs~ra~ed in the accompanying diagram (~Fig. 3).

Since, in Oc,~,otl~e,ra., adjacent chromosomes regularly pass to opposing poles, an orderly separation of the two complexes is assured except at; the separation nearest the cross-over in the "interstitial" segment. At this point the chromosontes may become oriented iu either of two

B C 4,1 J.x XlZ ,, 4 ' I 2.Y

4"3 "~ 2"--Y I~ 4 '3 ,-x i -Z

4.1 4-3

4'3 3.2 X Z a /~'1 1"2 X ' ] d

D E ~ig. 3, A. A diagram illustrating the postuIatcd pachygene association of chromosomes

in Oe. l)ratb~coh~ E tyl)ica.. The pMred regions of the chromosomes are considered str ict ly homologous. Chromosomes of the two complexes are designated by the symbols ~, and ft. The numerMs l, 2, 3, 4 and the lel~ters X, Y, Z designate the ends of specific chromosomes. The remMning ictters, r/iR, f/F, p /ps , refer to the positions of the hegerozygous genes witlfin the chromosomes. The ligh~sly shaded areas in ~shc middle of etu'omosomes 1.2 and 2 . x represent the " in te r s t i t i a l " segments , or the regions in which these two chromosomes are homologous, A elfiasma has been intro- duced iu tlfis region to mark the position of a cross-over ti 'om which the " n e w " chromosome, 2.3, arises. ]3 ,rod C represent possible bypes of dis junct ion of chromo- somes in the first meiotic division following cross-over in the " in te r s t i t i a l " region provkled the spindle a t t achmen t i~ to t;he lef t (in the dLugram) of the cross-over. The fol]owing eight products should occur:

1.4, 3 .x , r emaimng ~. chromosomes ... 1.4, 2 .3 ; remaining cz chromosomes ... 3.4, 1 .x , remaining fl chromosomes ... 3 .4 , ] .2, r emahnng fl chromosomes ... 1.4-, 2.3, r emaimng fl cl~'omosomes ... l ,4, 3 .x , remMning fl chromosomes ... 3 .4 , 1.2, remMnmg ~. chromosomes ... 3.4., 1 .x , remMnmg ~. chromosomes ...

inviable duplication x , deficiency 2: viable f~," of /br,mosa; viable Ffl" (not observed); inviable duplicat ion 2, deficiency x ; inviable duplication 2, deficiency x : viable fl of t!ll)icn; viable ~ of typicc~; inviable duplication x , deficiency 2.

]) a,ad E are the same as ]3 and C, excep~ t ha t the spindle a~achmen6 is Laken to tile righ~ of tile cross-over from which bhe l'eeovera0~le products are equiw~.lenl, to the eight lisLed under B and O.

330 A (~e~,etic c~d Cytological, A'~zal,y,vi,~' o f O. pr~gincol~

positions as illustrated in 13 and. C of Fig. 3 (or in D and E of the same figure). As indicated in the legend to Fig. 3, four viable combinations of chromosomes (complexes) may result: the characteristic ~. of l)rc~ti'~b- co~, blte characteristic fi, the modified f~' el:' mug. Jb,r,m.osa., and ,~ modified Ffi' complex which has not so far been observed.

The frequency of crossing-over in the "interstiti,~l" segment cannot be determined directly. The linear order of Cite megasporcs resnlting from the chromatid disjunct~ion illustrated in Fig. 3 ]3 (or E) may be any of the following (in which x indicates an inviable complex):

(1) ~. '--x--x--r/~'; (a) x--~.'--F/3'--x;

Cytological observations on other species of Oe,~othe~'c~ (genner, 1921; @erl~ard, 1929; ]tudloff, 1.931) indicate that the embryo sacs invariably develop from the megaspore at one end of the linear series or ~he other (i.e. either the micropylar of cilalazal megaspore) and not from the megasporcs in the middle of the linear series. Of the megaspores in the end-positions, the mieropylar megaspore ordinarily develops into the embryo sac milers one complex has a physiological superiority over the other, in which case (]tenner, 1921) the megaspore carrying the favoured complex %notions whether it is at the micropylar or chalazal end of the series. In p~'~ti~zcola tyl)iccr, the ~ complex has this physiological su- periority over the fl complex as witnessed by the %nctioNng of ~ in about 90 per cent. of the eggs. The superiority of f~' over/3 in nmt. ./b~'~zosc~ is of a similar magnitude (85 per cent. observed). I t may be inferred that f~' has a similar superiority over Ffi' and the inviable complexes designated x. Hence, from megaspore tetrads (1) and (2) we may expect f~' to function in the majority of instances, whereas from tetrads (3) and (6) fc~,' should never fnnction since it is not present in one of the end megaspores. So from the type of disjunction illustrated in Fig. 3 B, f~.' should be recbvered in something less than half of the instances. However, this type of disjunction (Fig. 3 B or E) should occur only half thg time; and the type illustrated in Fig. 3 C (or D) should occur half of the time. From the latter type f~' cannot be re- covered. Hence, following crossing-over in the "interstitial" segment, the fc~' complex offo~'~'~osc~, should be recovered in something less ~han one-quarter of t,he instances. The observed frequency of mntationfo~',mos~ in approximately 1.3 per cent. must indicate a mimmum frequency of 5.2 per eene. crossing-over in the "interstitial" region, which is equi- vMent Co 2.6 per cent. of recovered cross-overs from ordinary set-ups.

~TERLINCI E!~'IERSON 331.

~c ~ [ N T E I ~ S T [ T I A L S E G M E N T S ~'

]a the ring chromosomes of Oenothera, no one chroalosome is strictly homologous to any other, but each chronmsome must be homologous over different parts of' its length to regions of two different chromosomes. For example, chromosome ] .4: of' the fi complex of pratincola must be homologous at one end to part of chromosome 1.2 of ~, and at the other end to a region of chromosome 3.4 of the z. complex. Darlington (193], 71932) has reasoned that the large number of' trauslocations necessary to produce a ring of fourteen chromosomes from an all-pairing form should result in chromosomes of still greater mixed homologies. Chromosomes 1.2 of ~ and 3.x of/? may be taken as an illustration. The former has one end homologous to part of ]. ~ of fi, the other end to part of 2 .y of fi, and a section near the middle homologous to part of chronmsome 3.x of ft. Darlington (1931) Lad cytological evidence for the presence of "interstitial" segments in Oenothera,, but h/ his examples it was im- possible to determine the particular chromosomes involved.

Such "interstitial" segments have been demonstrated in other plants. In Pisv, msa, tiv'u,m, Sansome (1932, 1933) found chiaslnata persisting in the mid-regions of two chromosomes in a ring of six in which the chromo- seines involved were separated by two other chromosomes. One of the descendants of the plant with the ring of six chromosomes was observed to have a ring of four chromosomes. Sansome's interpretation that the new type resNted from crossing-over in the "interstitial" region is the same as that just offered to account for the occurrence of naut. Jbrmosa. In Sansome's ease the evidence fox the presence of the "interstitial" segment came in part from direct observation of ehiasmata in that region and in part from the altered configuration in the descendants. In the case of Oc. l)ratincola, no direct cytological evidence that the chromo- somes do pair in the "interstitial" region was obtained. However, as shown above, it has been possible to determine both genetically and cytologically the partieNar chromosomes which must have this segment, wl~le the frequency of crossing-over within this segment is indicated by genetic tests. Somewhat similar examples in Zea and Datura have been reviewed by Sansome (1933).

Darlington's further suggestion (Darlington, 1931, 1932) that most ring chromosomes in Ocnothera have "interstitial" segments near the spindle attachments, in which the genes characteristic of the complexes are located, and in which crossing-over does not occur, was objected to by Emerson (1932) and by Rennet (1933). These authors believed that

332 A Genet'ic a n d Cy to log ica l A~a, lys i s of O. p r ~ t i n ~ o l ~

most of {:he genes eha,racteristic of t he complexes mus{: lie in {:he dis[;al arms in which crossing-over does not disturb the end-homologies of the chromosomes (see Fig. 2, p. 318) to sa,tisl!y {:he genetic observations. This objection was not extended to ~pply to {:he presence of "inters{:itia]" segments as such. Since the origin o1~ mu{:../brmosa is ascribed to one such segment, it is of in~erest to know how frequent such segments may be in the Oenotheras.

Oe,nothc~'a bie~mis (cdbica,,n,s .~'ubens) has two rings, one of six and one of eight chromosomes. Presumably the two rings act i~nde]?endent;Iy in the meio{:ie disjunction of chromosomes, and four types of gametes (con:rplexes) should be produced: {:he albica~,s and 'rubs,as complexes ~nd two others ran, de up of' chromosomes belonging in pgr~; to each of these. However, these two mixed complexes never appear a,mong {:he func- tioning gametes, and[ we must conclude that they axe in viable. I t seems highly probable {:hat the failure of these {:wo types to survive is due ~o "insterst i t ial" segments so arranged that the mid-region of an albiea~zs chromosome in. one of the rings has its homologous region in one of {:he ~'.ube'ns.chromosonms in the other ring. Then if the two rings are assort, ed independently, two of the resulting types should be unbala,need for this region (i.e. this region would either be presen{: in duplicate or not a~ all). Since 'm~bri,n,e~'vis recurs fairly frequently (one per thousand), it is possible tha t it arises in ~he manner postulated :for {:he origin of mug. formosa,, in which ease there would be three known instances of the occurrence of interstitial segments in Oe~,othe~'a,: one in ca, oh of p'rati.ncola., bie~,~is and Lama,'re]cia,~.a,.

Ig is also important ~o know which chromosomes do not carry "inter- sl~itia,l" segments. In Oe..pra, tincola,, chromosome 3.4 may be shown not to have such a region, since in the formation of f~' it in replaced by parts of chromosomes 1.4 and 3 .x, fi chromosomes adjacent to it in the ring. I f there was a region in t, he middle of 3.6 homologous to some region in any other fi chromosome, the new i~' complex would be deficient for tha t region and consequently non-functional as "~ ga,mete. The same might be shown for terra.in chromosomes taking p~u:f, in the production of h alf-mutants in Oe.. La,,m,a~'cl:ia, uc~; but in these insta.nces the particular chromosomes involved have not been iden{:ified.

I n ' a n y hybrid having the configuration a ring of twelve and a pair in which, by mea,ns of heterozygous genes, it can be shown that the pair segrega{:es independently of {:he complexes in the ring, it is evidenb that, no la,rge par{: of t;he paired chromosome is an " inters t i t ia l" segment homologous to par{: o[' any chromosome in the ring. The same is t~rue

ST]~.t%LING EMEP~SON 333

for hybrids with a larger number of chromosome pairs provided each pair can be followed genetically. As examples of this sort the following may be mentioned: chromosome 1.2 can have no segment in common with any other chromosome in ~,elans.rubens and in hHoolceri.'rube'ns; chromosome 5.6 is completely independent from all (i.e. has no region in common with any) other chromosomes in.flavens, rubens, hHoolceri, rubens, and fl, avens.ga, udcns; in fla, vens ./fiectens, chromosome 2.3 is independent of all other chromosomes, and the two remaining rings of six are inde- pendent of each other. The observations upon which the above state- ments were made are summarised by i~enner (1933, pp. 237-4-3). Earlier in this paper it was shown thai) in the hybrid .flavens.fi, two pairing chromosomes (1.,t- carrying f, and 7.8 carrying B) segregated inde- pendently of the ring of eight chromosomes and hence are free from interstitial segments.

Darlingtmfs arguments for the presence of a large nmnber of "inter- stitial" segments in Oenothe~'a were somet/hing as follows:

(1) The ancestral form of ~he ring-forming Oenotheras was an all- pairing form.

(2) Repeated reciprocal transloeations gave rise to rings containing larger and larger numbers of chromosomes.

(3) These transloeations must have been distributed more or less at random throughout the chromosomes involved, and whenever two different transloeations involved the same chromosome an "interstitial" segment must necessa,rily be produced.

(4) The ring chromosomes of Oenothe,ra pair and cross-over in the homologous end-segments and hence should soon become homozygous for genes located in the end-segments, consequently the genes which maintain their hegerozygosity must be located in the "interstit ial" seg- ments where crossing-over does not ordinarily occur.

Certain aspects of Darlington's general argument seem to me to be more readily justified than others. The differenb points can best be discussed separately.

(1) With one exception, the races of Oenot/ze~'a native eo California so far studied have been found to have all-pairing chromosomes (Cleland, 1933). Furthermore, the chromosomes of the different races have been found to be practically identical in their "end-homologies". Most of the races so far examined by Cleland have the chromosomes listed earlier in this paper for l~.[rancisea,~,a. The only other arrangement found is that listed for l~Hoo/ce~.i, and this differs only in two chromosomes having 7.8 and 9. ] 0 in place of 7.10 and 8.9. If the hybrids with the CaliNrnia

33~1 A Genetic and Cytological ~/tnaly~is of O. pr~ t inoo la ,

species are reviewed, it is noted tha t chromosomes with end-homologies identical to those of hfrancisca'na and hHookeri ocem: very generally as indicated in Table I. Furthermore, it can be noted that those complexes which are most different from these two are generally :found to be very different fl'om each other (Table II). These two observations agree with the assumption tha,t ~,he ancestral form of most Oenothe~'a, species had

TABLE I

A list showi'~g the relatively wide distribution of chromosomes homologous to those qf hHookeri and ~ffraneiseam~ as indicated by the pairing of chromo- som.es 'i'n tl~e hybrids

l?~irs with _ _ 2 . _ _

Species Locality Complex ~Hoolceri cana. Aul,hority strigosa Wyoming st.ringe.~a~ :3 ? Cleland and BtM~eslee (1931) Coc/,~erclli Colorado elongans ? l Emerson (1931 b) " W " Wyoming \'V-/3 ? 2 Stm%evant (unpub.) chicagincnsis Illinois cxcctlc~s 5 7 Clelaud and Blakeslee (1930),

impact.Morns 2 1 Emerson (1931 b), Cleland (1033)

Tracyi (?) Alabama l (u -~ 3 3 Sturtevanl~ (unlmb.) Ku-fl ? 0

fp'a,'ng~flora Alaba.ma acuens 3 5 Cleland and Oehlkers (1929), t,ru.ncans 0 0 Cleland and Blakeslee

(1930), Clela.nd (1933) l)ratincola Kentucky prat. c~ 3 5 TMs l~aper

p. ra~. fl 2 1 £'hulliana. New Jersey 3ugens 1 2 Stm'tev~nb(1931and unpub.)

macula.?t s 1 ? " G " New Jersey G-~. ? 1 Stm' tevant (unpub.) Oalcesia.mL Long Island accclera'ns 1 l Stur~evang (unpub.) " N " Long :Island ¥ - f l 0 ? S tur tevant (unpub.) nobska Massachusetts pubens 1 ? Stur tevant (1931) " K " Maine I ( -~ 3 ? S tur tevant (unpub.)

K-J3 2 ? Lamarck, ia'na (Europe) vclans 5 4 Clelandand]31~keslee(1930),

flaude'ns 2 2 Sturt;evanfi (1931), Emerson (1931 b)

suaveolens (Europe) Jlavcns 5 3 Cleland and ]31akeslee (1930), albica.~s 0 l Emerson (1931b), Sturte-

r a n t (unpub.) .m~'icata (Em'ope) rigens 4 3 Cleland (1933), Stur tevant

curvct~s 0 ? (unlmb.)

pairing chromosomes, and that these must have been very similar ~o

those now found in ~francisca, na and 1~Hooke,ri. (2) If we grant that the parental form had a]l pairing chromosomes

it is necessary to assume that nmnerous translocations have taken place

to give rise to the present-day ring-forming species. (3) Artificially induced translocations in Z, ea Ma,ys seem to be dis-

tributed more or less at random throughout the chromosomes (E. G. Anderson, unpublished). I f one were go build larger chromosome rings

STEgLINO Eh'[ErCSON 335

in Zea by in~,ercrossing different reciprocal translocaSions, each ring of six chromosomes should have one " inters t i t ia l" segmenb (see Brink and Cooper, 1932), a, ring of cigh[ should hays two and a ring of fourteen should have five such segments, or possibly more, a,s has been pointed out by Darlington (i932). There are, however, other organisms in which the positions of the translocations in the chromosomes do not seem to be clisl;ributed at random. Ill C,re'pis, Lewi~sky and Arara~ia,n (1.931) lbund tha t the chromosomes broke at the locus of the spindle at tachment much more frequently than was to be expected if {~he breaks occurred at random. In D,rosophila, Patterson et al. (193~1) found tha t the two chromosomes (II and III) with median spindle at tachments tended to break most frequently either vary near the spindle at tachments or very

TABLE II

A list showi'n 9 the .nt~mber of chromosome ya.b's in hybrids between coral)fezes ha vi~tgj'cw chromosomes in common with either hHookeri or l~franciseana

accelera~s.gmldens . . . 2 p a i r s ... 8tnlrt, evan l ; ( t 9 3 1 ) accelera*ls.jugens . . . . . . I p a i r ... ]bid. accelcra~s.'mac,shu~s . . . 2 p a i r s . . . Ibid. albicmts.elo~lgo.~ts . . . 1 p a i r . . . C l e l n n d a n d O e h l k e r s (1929) albica.'~ls.gaude~zs . . . . . . 0 p a i r s . . . C l e l a n d (1928) (dbica~ls.1)'w~lctulans ... 2 p a i r s . . . C l e l a n d a n d B l a k e s l e e (1930) ga,tcdc~ts.jugens . . . . . . 0 p a i r s . . . Sgu rgeva ,ng (1931) flaudens.p~nct,Mans . . . 0 p a i r s . . . C l e l a n d a n d B l a k e s l e e (1930) ga'nde~ls.lru'nca'~s . . . 0 p a i r s . . . Clela, n d a,nd O e h l k e r s (1929) j,~gc~s.,mac,Ma~ls . . . . . . 0 p a i r s . . . St,url~evan~, ( 1 9 3 l ) .mac~dans.l)w~clldans . . . 0 p a i r s ... S tm ' l ; evan l , ( u n p u b . )

near the distal ends. In Oenothera there is no clear evidence to show whether or not the translocation points are distributed at random in the chromosomes. 1 In the absence of such direct evidence we sllould assume tha t the c]lronmsome breaks most likely do occur at random, were it no~ for the evidence available from Crel)is and Drosophila showing tha t this is not necessarily the only possibility. I f a disproportionately high percentage of the breaks occur a,g or very near the spindle attach- meng in Oenoahera,, the number of " inters t i t ia l" segments expected may be greatly reduced. I t is also possible that translocations in which the chromosomes are broken near the distal ends in Oe'nothe,ra would tend to be eliminated. I f the regular zig-zag disjunction of chromosomes in meiosis is conditioned[ by chiasmata, as postulated by Darlington, very short end-segments should have a decreased chiasma frequency leading ~o increased non-disjunction and increased sterility. The greater sterility

.t T h e f a s t {,h~t~ Oclwthera, c h r o m o s o m e s h ~ v e m e d i g m s p i n d t e a~, t ,aehment , s a n d ghag

t;hm:e i s liI)l)le s i z e d i f f e r e n c e be{~ween t h e c h r o m o s o m e s s e e m s go indio~l ;e lbhat~ 6 r a n s l o c a g i o n a

h a v e nob o e e m w e d ab r ~ m d o m ghroughou l~ ~he c h r o m o s o m e s .

336 A Ucnel, ic c~nd Cy~ologiccd, An~,dy,~i,s' of O. ]?rabincoh~

would place forms heterozygous for such translocations at a great disadvantage.

(4:) I~enner has shown that the ring-forming species of Oeno/,hcra, are hetcrozygous for two complexes. These complexes differ not-, only in the a,rl/angemcnt of homologous end-segments i)ut, also in the genes carried by each. The breeding behaviour indicates thai, mosl; of the genes cha.r~c- t;ersi|:ic of {;he complexes must lie in I~he end-segmcn{,s of I;hc chromosome (l~,enner, 1933; ]~3merson, 1932), since l;hey arc occasionally tr~msferred ['rom one, complex I~o another by crossing-over wi/,houl, altering the end homologies of the chromosomes (see I~ig. 2, p. 318). This obser~a.tion raises a furbhor question: since t~hc heterozygous genes characCerist~ic of the complexes can become homozygous by crossing-over, why ha.re I;he species of Oe/Jw~he~'c~ not become completely homozygous t'or genes carried? The answer to this may be that, the present-day species of Oc'~wthe,ra are of much more recent origin than has been mtpposed. Several general observations lend support to this assumption. ~ [n the first place, while the small-flowered, ring-forming Oenotheras are gene- rally self-pollinated, we have observed that many flowers are e~feetively emasculated by insect larvae (a rhyncophoran larva in eastern North America and a lepidopteran larva in sou~h-western North America). The st~yles and stigmas of such emasculated flowers arc often uninjured, and a good set of seeds may be obtained by cross-pollination. Hence even in the normally self-pollinated races there is a "mechanism" for cross pollination, provided more than one race of Oe~othe,ra is present in a given locality. The second observation deals with the variable and shifting nature of Oe~'~othe~'a populations. To-day we find Oenotheras growing commonly in the following habitats: sand dunes and sandy shores of lakes and along the sea coast, river bottoms, railway embank- merits, and idle agricultural fields two or three years after cultivation has ceased. In general, Oenotheras are go be found in fairly light soil from which the competing grasses and other plants have been removed either by cultivation or by movements of the soil itself ~hrough the agency of wind or wager. I t seems probable that the Oenotheras have extended their range somewha~ since the advent of ~he whi~e man go North America due go the extensive cultivation of vast tracts that had previously been either woodland or grass lands. Observation over a

* Some of the observal,ions reporl, ed here have been made by Prof. A. H. Sburgewml,, wi{,h whom I have discussed ~his problem, ~md who has Mndty permitted me go make use of his obserw~ions on this general problem as well as certain unpublished data eit, ed ea.rlier, t ~m ~lso indebted 1,o Dr. G. W. 7BeadIe and Prof. Th. Dobzhansky for criticism rehousing go t,his section of the paper.

~T+I~3I%L.[N (21 ])]M.EI+SON 007

period of four or five years often shows a marked change in the Oenol, he,rc~ population within a lhni~ed area,. I have not±iced such changes a~ a st,at,ion l~went,y miles west of Ann Arbor, Michigan, and Prof. Sburgewmt~ nobed similar changes near Wood's Hole, Ma, ssach.uset,t,s. I imagine t~he experience is common t±o slmdent, s of Oe.~wl/t,e,r~ who have eoltecl;ed tnal~erial repeat~edly from the same localil~y. These changes in popular,ions may t+,ake {,he form of ehe disappearance of all 0enot±hera.s from IJm locality, I,he disappea.ra, nce of only one or more forms, or possibly {~he appearance of differ<~nl, [orms. Since t, he Oenol~hera.s seem 1+,o occupy a limit,ed area. for a few years only, and since cross-pollination may occur fairly oft;en, it; is possible ~,hat± nm.ny o[ t+,he :f'm:ms t±a,kett in{;o e+ulgival~ion have had a recent, hybrid origim Once a race is trader euldvagion t±here is a, more or less conscious selecl;ion l~o "I~ype" by f, he i!~vesgiga~or which may help t~o preserve t±he hybrid nat,ure of t,he ra.ee.

.I:f one grant's t,he supposit,ion l~hat± most Oenothc,ra, races are of recent, hybrid origin ig is possible t,o account for t,he het,erozygosit±y of t,hese races wit,hot,t, recourse 1;o "interst, i t iM" segment's, and, at; elm same t,ime, ¢,o a, ccount, for t,he observed genet,ic behavionr of t,hese races. We know definilMy t±hag "interstit ial segments" do occur in some chromosomes of particular Oenot±heras. We a.lso know, from analogy t,o C,rcpis a, nd D~'osql)hila,, t,ha~ t,hey need not occur as frequent, ly as had been supposed. That, t,hey are definit,ely not, responsible for most, of t,he gene differences distinguishing t,he complexes of t,he various races is shown by t,he breeding behaviour of t,he races t,hemselves.

T H E DIFFERENT REVOLUTE-LEAVED 5tUTATIONS OF OENOZ'HE.R.d PRATIN(YOLA

The analysis of t,he changes ocem'ring in t,he product,ion of rout,. ]b'mos<~, from prati~molct E typica has been based primarily upon t,he study of one plan++. In t,he cult,ure of Oe. p'rati,~tcoh~ grown in 193~I Shot,her exampte of t,his "rout,salon" appeared which proved t,o have t,he altered chromosome configurat,ion (a ring of t,welve and a pair) already reported. The int,erpret,a,t,ion out,lined in this paper is in agreement' wi++h t±he generic findings of Blanehgrd (Cobb, 1921; Blanchard, 1929).

Mutant,ion setacea.,has been considered by Blanchard (].929) t,o be ~he homozygous, fl,fi segregant, ti'om Oe. p,ratincoh~. All my observat,ions support' t,his conclusion. I have not,ed t, he differences bet,ween t,he ~ and fi ~wins in out,crosses t,o ninny unrela~ed species a, nd ~he differences charac- teristic of ~,ihe fi twins are exaggcrat,ed in rout±, selacea. Among t, hese difYerences, t,he mid-rib hMrs are no~eworl~hy. In out'crosses go Oe.

338 A 6~e~~etic c~,),d Cytol, ogiccd A'~c~lysi,s o f O. pr~,ginoob~

Hoolce.ri and ~o Oe. fra,)~,dscc~,~,a,, for example, the ~, l)wins have erect mid-rib hairs and the fl twins have these hairs more or less decumbent. In rout. setacec~ the mid-rib hairs are completely prostrate (Fig. ~[). Further, from such fi twins in outerosses, typical mug. 8etctcect generally appeared as a segregant in/~'~ (see Fo from./l, ctve~,s, fi and from cdbicc~.r~,,s, fi, p. 325). Mul~ation 8cta, cec¢, should have seven chromosome/?airs, but it has been impossible thus far go obtain good cytological preparations.

]t~ig. d:. Blid-rib h~irs of different Oenotheras , :-, 25 ~t)proximately,

Mutation ~'cta, cec~ is a very weak " r u n t " rarely flowering under our conditions of culture.

Mutation ~'evol,~.~tct has appeared ~hree times in my cultures. Each plant has flowered very late in the season, and it has been impossible go obtain buds suit'dfle for cytological studies, or go obtain seeds ik'om either self-pollination or outcrossing, so tha t the nature of the changes accompanying the appearance of this form could not be de~ermined.

Mutation cdbica~s has appeared once in my cultures, but the plant couId noC be brought go maturity. [[~ is possible go speculate as to the

STEI%LING EMERSON 339

nature of the origin of the ]ast two revolute-leaved mutations but in the absetaee of any direct information no good[ purpose would be served.

~ I~{ASS M.UTATION '~

As pointed out by Blanchard (1929), the mass-mutating strain of Oe. ln'c~ti'ncolc~ (Bartlett, 1915) differed from the non-mass-mutating only in the relatively greater frequency of the homozygous /9./9 segregant, setacecL, and the decreased frequency of tyl)'ica. There was also a great increase in inviable seeds in the mass-mutating strain. I t would seem that in this strain the fl complex must have served[ as eggs nmeh more frequently than normally. Since the mass-mutating strain has been lost it is impossible to obtain more data on this phenomenon.

SU~r~,~ABY A~D CONOLUSmNS

A new occurrence of ]nut. fo~',m.osc~ together with the parental form, Oe. In'ctti~cola, E tyl)icc~, and hybrids of both with other species were studied cytologically and genetically ~o determine the nature of the changes occttrring when mut. fo~'mosa is produced.

The egg complex, g, of tyl)ica was found to have chromosomes 1.2 (carrying R, the gene for red nerves), 3.4 (carrying p, non-punctate, and probably carrying the normal allelomorph of f), 7.10, 8.9, 11.12, and either 5.14 and 6.13 or 5.13 and 6.14.

The pollen complex,/9, of tyl)ica was found to have chromosomes 1.4 (carrying I, the gene for revolute leaves), 7.8 and 13.14, with the re- maining chromosomes undetermined but wRh ~he gene ps (punetate stems, striped bud cones) in the 3-end of a chromosome designated 3. x.

The egg complex of mut.fo~'mosa, fc,.', was found to have five chromo- somes in common wRh ~ of l, yl)iCa, but chromosomes 1.2 and 3.4 have been replaced by 1.4 (carrying f) and 2.3 (carrying R and ps). In this replacement, chromosome 1.4 has come directly from/9 of t, yl)icct, while chromosome 2.3 represents a new chromosome made up of the 2-end of 1.2 from ~ and the 3-end of 3 .x from/9.

The regular occurrence of nmt. fo~"mosc~ with a frequency of about thirteen per thousand in the progeny of typicc~ is accounted for on the assumption that the mid-regions of chromosome ] .2 of ~. and 3 .x of/9 are homologous and occasionally cross-over. The distribution of such "interstitial segments" in Oe~ot,/~,e~'c~ chromosomes is discussed.

Further evidence is presented tending to show that rout. se, tacec~ is the homozygons [3./9 segregant from t~y~)ica, a conclusion already reached by Blanehard (1929).

J o u r n . of Gene t i c s xxxf~ 22

340 A Genetic and Cytological Analysi~ of O. pr~tincoI~

~EFEI~ENCES

B~A~rL~TT, H. I~. (1915). "M~ss nmt~tion in Oenothera pratb~cola." Bet. Gaz. 60, 425-56.

]315~OgA~o, F. C. (1929). "The geuegical consgigution of Oenothera 2~ratincoh~ and its revolute-teaved nmtations." J. Wash. Acad. Sci. 19, 1t5-25.

BmNK, I~. A. and CooPn~, D. C. (1932). " A str'*ill of maize homozygous for seg- mental interchanges involving bo6h ends of the P-B,r chromosome." Prec. nat. Acad. Sci., Wash., 18, ~I~11-7.

CL~r~AND, If.. E. (1928). "The genetics of Oenothera in religion go chromosome be- haviour, with special reference go ccr|;ain hybrids." Verh,. V. -i'n~. Kongr. Ve~'erb. (Z. O~,dulct. Abstamm.- ~,. VererbLeN'e, suppl. 2), pp. 554:-67.

- - - - (1933). "Predictions as go chromosome configuration, as evidence for segmental intercha.nge in Oenotheru." Amer. Nat. 67, 407-18.

CLESA~D, i~,. E. and B s ~ _ ~ s r ~ , A. F. (1930). " In terac t ion between complexes as evidence for segmental interchange in Ootothera." Prec. nat. Aged. ~5'ci., Wash., i 6 , 183-9.

- - - - (1931). "Segment,~l interchange, the basis of chromosomal ~tgaehments in Oenothera." Cytologia, 2, 175-233.

GLELAND, ~. ]~. %nd OEIYLKERS, I i~. (1929). "New evidence bearing upon the problem of the e3~ological basis for genetieal peculiarities of the 0enothera.s." Amer. Nat. 63, 497-510.

CosB, F. (i921). " A case of l~Iendelian inheritance complicated by hegeroggmegism and mutation in Osnothe~'a g)ratincola." Genetics, 6, 1-42.

C o ~ , I0. and ]3Ag~n~'rw, I-I. H. (1919). "On Nendelign inheritance in crosses between mass-mutating and non-mass-muta~h~g strahm of Oeuotherc~2~ratincola,." J. Wash. Aged. Sci. 9, 462-83.

D,a~r~c~'ro~, C. D. (1929). "I~ing formation in Oenothera and other genera." J. Goner. 2 0 , 345-63.

- - (1931). "The cytological theory of inheritance in Oenothera.." Ibid. 24, 405-7~t. - - (1932). "The behaviour of interchange hegerozygogcs in Oenothera." P~'oc. nat.

Acad. Sci., Wash., i 9 , 101-3. Es[nnso~, S. (I931 a). "Ttte inheritance of certain characters in Ocnothera hybrids

of different chromosome configurations." Genetics, i 6 , 325--~8. - - (1931 b). "Genetic and cytological studies on Oenothera. II. Certain crosses

h~volving Oe. rubrica, lyx and Oe. ' fl'a, nciscc~nct, ~ulfurecd." Z. indukt. Abslamm.- u. VererbLehre, 59, 382-9~L

- - (1932). "Cln'omosome rings in Oenotherc~, D~vsoT~hilct and mMzo." Pros. nat. Aged. Nci., Wash., t 8 , 6 3 0 - 2 .

E ~ s o ~ r , S. and S'rua'r~va~'~', A. H. (1931). "Genetic a.nd cygologieal studies on Oenothera.. III . The transloeation interpretation." Z. i'ndulct. Abstamm.- u. VcrerbLehre, 59, 395-419.

(1932). "The lh~kago relations of corgMn genes in Oenothera." C, cnetics, i 7 , 393~I12.

G~n.mx~D, K. (1929). "Genetisehe und zygologisehe Untersuehungen an Oenothera grandiflorc~ Air." Jena,. Z. Naturw. 6g, 283-338.

t r " " I STERLING E~'IE RSON 341

I.([mm~lqg C. G-. (1929). "h'[eiosis ill pollen mother coils of strMns o[ Oenothera 2)ratincoh~ B~rglett." Bot. Gaz. 87, 218-59.

LEWI'rSKy, G. A. and Am~mkT1~kN, G'. A. (1931). "Transformation of chromosomes under the influenco of X-rays." Bull. a,~)l)l, l~ot., aeuet. Pl. Breed. 27, 265-303 (English summary).

PAT'rl~I~SON, J. T., STO~E, W., 13EDmaEI;, S. and S eeriE, B![. (193~). "The production of tmmsiocations in Drosoph,ila." Amer. Nat. 68, 359-69.

/~Nm~m, 0. (1921). ":H:eterogamio im weiblichen Geschlecht und Embryosaek- bildm~g bei dea 0enothcren." Z. Bot. 13, 609-21.

- - - ( 1 9 3 3 ) . "Zur Kentnis dor Legaifakgoren und des Koppelungswechsel der 0enotheren." Flora (N.S.), 27, 215-50.

I~ENNER, O. all([ CLEL~ND, ~. E. (1933). "Zur Gelmtik urn1 Cyto[ogie dor Oenothera chicaginensis und ihrer AbkSmmlinge," Z. indulct. Abslamm.- u. VererbLehre, 66, 275-3t8.

Rm)LOF~', C. F. (1931). "Zur Polaris~giou in der Reduktions~eihmg hegerogamer Oelmtheren. I. Die Embryos.~ck-Entwicldung und ihr6 Tendenze, n," Ibid. 58, 422-33.

SANSO~E, E. 1~,. (1932). "Segmenta,1 interchange in Piswm, sativ~m." Cylologia, 3, 200-19.

- - - - (1933). "Segmental interchange in Pisum. I I . " Ibid. 5, 15-30. Sgurm, G, H. (1923). "Linkage with lethal factors the solution of the Oenothera,

problem." Euge'~ics, Genet. and the Family, i , 86-99. STaDLE~, L. J . (1933). "On the genetic nature of induced mutations in plangs.

II . A haplo-viable deficiency in maize." l?es. Bull. Mo. agric. Exp. Sta. No. 20~1, 29 pp.

STU~TEW~T, A. H. (1931). "Genetic and cytological studies on Oenotherce. L Arobs]ca, Oa/~',csian~, Ostraea, Shulliana, and the inheritance of old-gold flower-colour." Z. indulct. Abstamm.- u. VererbLehre, 59, 365-80.

DE V~Es, I-I. (1919). "Oenothera rubrinervis, ~ half-mutant." Bot. Gaz. 67, 1-26.

A P P E N D I X

In this section additional genetic data are presented. These data are in agreement with the interpretation already presented and help support that interpretation. They are presented here and not in the text since ,they are not necessary to the development of the argument and show little of anything in addition to the data already quoted.

~Iut. formosa × Nd~, F~ re.'. lg~ has chromosomes 1.2, . . 3, 3.4, 1. ~ in a ring of four and all heterozygous genes (R, v, pr, n, i) should be linked. /~'~ culture 2580 of 1933 gave the following:

R V ps iN" f 16 (homozygous for genes of f~') R V pr N F 127 (the #t type) r v P~ n F 205 (homozygous for genes of Nd')

RVPr l~i i} iq V :P~ iN F (cross-over types) r V ISr N F r v prNF

357 22-2

362 A Geese, tic a~zd @tologiccd A~cdysis of O. p n ~ g i n c o l a

The data show linkage between all genes. Unfortunately, ~he cross-overs recovered in Pc data do not help in determining the position of the genes in t, he chromosomes, since practically each recovered type may represent one of two possible cross-overs. For example, R V pr N f may be either f~, .pr_f~, or I~ ' . i -N~. In a back-cross to Nd ~, representing a back-cross for r, n, and v, there was one cross-over f n V, in 115 plants. This must represent a cross-over between v and the ~ransloeation point if v is in arm 1, or between v and r if v is in arm 2. In a back-cross to r, la, i, there were four cross-overs, 2 F II ps and[ 2 f r pr , in a ~,otal of 228. These must have all been cross-overs in arm 3 between pr and the transloeation point.

From the i~lJlave~s, fl in which ~ should he in the pairing chromosome 1.4- and B in the pairing chromosome 7.8, with the flc~ve~,s zygotic lethal in tlae ring of eight, the following dat~ were obtained. In i/~ 2 there were 392 flat-leaved plants and 87 revolute. Among 221 of ~he flat-leaved plants, 123 had broad leaves (B) and 98 had narrow, and all were of the eonstitutionJlc~ve~zs.~. Of 43 of the revolute-leaved plants, 61 were .flc~ve'~s.fl and 3 were fi.fi. In the back-cross to fl there were 201 flat- leaved plants and 122 revolute. Among 9'1- of the flat-leaved plants, 86 were flaveq~s, fi and 10/~./3, and among 35 revolutes, 33 wereflave~~s, fi and 2 fi.fl.

In the F~ from f~,'. elo~Nc~q~s in which chromosomes 2.3 and 1.4 are pairs and in which R and f should be independent, there were: 9 f R, 2 f r , 10 FIR, and 3 F r .

These data together with those presented in the tex t represent all ~hat have been obtained from the 2)~'ctti~zcolc~ hybrids.