Euphytica 104: 95–106, 1998.© 1998Kluwer Academic Publishers. Printed in the Netherlands.

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Plant aneuploids: Suggestions for their classification

A.K. Koul & M.K. Dhar∗Department of Biosciences, University of Jammu, Jammu-180006, India; (∗ author for correspondence)

Received: 25 March 1997; accepted 5 June 1998

Key words:aneuploids, nomenclature, trisomics, monosomics, gene content

Summary

The paper lists, defines and classifies all types of aneuploids known hitherto. Categorisation has been made on thebasis of the alterations of chromosome number and gene content. The change in nomenclature of some aneuploidshas been warranted by the fact that some names that are in vogue do not reflect the precise nature of the aneuploidand, are therefore, ambiguous. For these ambiguous terms new names have been proposed.

Introduction

Aneuploidy refers to the nuclear condition when thechromosome count is not exact multiple of the basenumber of the species. The term was introduced byTackholm (1922) following his studies on genusRosa.Aneuploids generally arise through the fusion of ga-metes, one or both of which are hypo- or hyperhaploid.Such gametes arise through anomalies in the meioticdivision accompanying gametogenesis. The anomalymost significant in terms of the differentiation of ga-metes with deviant numbers is, late disjunction ornon-disjunction of chromosomes during gametogene-sis.

Lutz (1909) was the first to report aneuploid chro-mosome numbers in two progenies of the interspecificcross betweenOenothera lataandO. gigas. After thediscovery of the ‘Globe’ mutant inDatura stramoniumby Avery in 1915, Blakeslee et al. (1920) producedvarious other aneuploids in this species. Realizationof the possible utility of aneuploids generated a spurtof activity, and as a consequence much literature hasaccumulated on the subject in the last 75 years (seeBurnham, 1962; Khush, 1973; Bond & Chandley,1983; Dellarco et al., 1985; Koul et al., 1995).

The term aneuploid was initially used for indi-viduals with one chromosome less or more than thestandard complement. The former were named tri-somics and the latter monosomics. Dyer et al. (1970)extended the term to cells and individuals where the

loss or gain involved even a chromosome segment.In this way, segmental aneuploidy was added to thegeneral category of aneuploids. Segmental aneuploidyrepresents heterozygosity for such deletions or dupli-cations whereby one or more acentric segments ofa basic set are added or lost. It also includes thosecentric fragments where new chromosome arm com-binations have been added (modified from Rieger etal., 1976).

The classification of aneuploids proposed by ear-lier workers revolves around the nature of change inchromosome number. In some cases, aneuploidy doesnot change the total chromosome count of the nucleus,but alters the number of specific chromosomes, thetotal remaining the same. Khush (1973) identified 31kinds of aneuploids. Since then, many more types havebeen discovered; the number has grown to 74.

The present paper aims at listing all aneuploidsknown hitherto at one place and classifying them onthe basis of their chromosome constitution and genecontent. Changes in chromosome number and genedosage may or may not correspond. For example,all secondary trisomics carry an isochromosome inaddition to the standard complement. In such indi-viduals the chromosome number increases only byone, though the genes located on the isochromosomeare actually represented four times. Should such indi-viduals be classified as tri- or tetrasomic? Similarly,individuals trisomic for one and monosomic for an-other chromosome do not register any change in total

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Table 1. Abbreviations used in designating aneuploids

Abbreviation Definition

Tri Trisomic

p primary

s secondary

t telo; telocentric chromosome

te tertiary

a acrocentric chromosome

i isochromosome

I Inversion

(I) Interchange

chromosome number. Yet they differ from the disomicwith respect to dosage of different genes. The namesproposed for such aneuploids by earlier workers do notreflect their true nature. We have made an attempt todo away these and other ambiguities existing in thenomenclature of aneuploids by classifying them on thebasis of changes in chromosome number as well asgene dosage.

Proposed classification

The 74 aneuploid types known hitherto have beengrouped into five categories. Each category includesone or more subtypes. Each aneuploid type has beengiven an abbreviation and a chromosomal formula.The formulae are based on the tomato system (Khush& Rick, 1967). In all formulae, 2n refers to thedisomic chromosome count; 2n + 1 and 2n− 1 there-fore, denote addition and deficiency of a full chro-mosome, respectively. Individual chromosomes havebeen numbered A, B, C — etc. Chromosome arms aredesignated AS.AL, BS.BL etc., L denoting the longand S the short arm. Addition of the whole chromo-some has been denoted as 2n + AS.AL, 2n + BS.BL,etc. Isochromosomes for the short and long arms ofchromosome A are represented as AS.AS and AL.ALrespectively. The telocentrics for long and short armsof chromosome A are represented as .AL and .AS.The tertiary chromosome involving chromosomes Aand B is represented as AS.BL suggesting that theinterchanged chromosome carries the long arm ofchromosome B and short arm of chromosome A.

Table 1 lists the letters which have been usedsingly or in combination for designating the aneuploidtypes. The idiograms of all aneuploid types have been

illustrated in Figure 1. The karyotype ofPlantagoovata (2n = 8), was used as an example. It was se-lected mainly because, the chromosome number of thespecies is low, all chromosomes are heterobranchialand are morphologically distinguishable from one an-other. Recently Raupp et al. (1995) have proposed anomenclature for the genetic stocks of wheat. Sev-eral conventions regarding the designation of aneu-ploids have been enumerated and rules of hierarchyestablished. These conventions and rules of hierar-chy have been followed in the present communication,whereever applicable.

As pointed out before, the 74 known aneuploidtypes have been classified into five main categories.These are listed below:A. Addition aneuploidsB. Compensation aneuploidsC. Deletion aneuploidsD. Two-in-one aneuploidsE. Pseudo aneuploids

A. Addition aneuploids

This class includes aneuploids which carry in additionto the standard complement one or more, chromo-some(s), chromosome arm(s) or parts thereof. Theextra elements exist as acrocentric, telocentric, meta-centric or isochromosomes. The addition aneuploidsare subdivided into following three types on the basisof the number of additional chromosomes.

I. Single chromosome additions.Aneuploids of thiscategory carry one chromosome in addition to thestandard complement. It includes a number of sub-types which are listed below.1. Primary trisomic pTri: An individual in which the

additional chromosome is one from the standardcomplement (2n + AS.AL).

2. Secondary trisomic sTri: A trisomic in which theadditional chromosome is an isochromosome forone chromosome arm of the standard complement(2n + DL.DL).

3. Tertiary trisomic teTri: The additional chromo-some consists of parts belonging to two non-homologous chromosomes (tertiary chromosome)of the standard complement (2n + BS.AL).

4. Telotrisomic tTri: These aneuploids have a telo-centric arm added to the standard complement(2n + .DL).

5. Inversion telotrisomic ItTri: The additional ele-ment in these trisomics is a telocentric chromo-

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Figure 1. Idiograms of different aneuploid types described. Abbreviations: p – primary; s – secondary; te – tertiary; t – telocentric, telosomic;i – iso, isosomic; a - acro; (I) Interchange; I – Inversion; Tri – trisomic; T – tetrasomic; P – pentasomic; Q – quadruple; H – hexasomic; O –octosomic; C – compensating; M – monosomic; N – nullisomic; (trp) – triple; D – di, disomic; d – double; (tet) – tetra.

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Figure 1. Continued.

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Figure 1. Continued.

some which is the product of pericentric inversionand misdivision of the centromere. The extra chro-mosome consists of segments belonging to botharms of the chromosome (2n + .DSDL).

6. Metatrisomic mTri: Aneuploid with an additionalmetacentric chromosome that is unlike any in thebasic complement, having arisen through struc-tural alteration of some chromosome of the stan-dard complement (2n + meta DSDL).

7. Acrotrisomic aTri: An aneuploid in which the ex-tra chromosome is acrocentric, having originatedthrough deletions of terminal end(s) of a chro-mosome of the standard complement (2n + acroDSDL).

8. Interchange primary trisomic (I)pTri: A transloca-tion heterozygote carrying an extra chromosomethe homologue of which may or may not be in-volved in the interchange (2n(TAL.BL) + AS.AL).

9. Interchange secondary trisomic (I)sTri: A translo-cation heterozygote carrying an additional isochro-

mosome for one arm of a chromosome involved intranslocation (2n(TAL.BL) + AL.AL).

10. Interchange tertiary trisomic (I)teTri: A translo-cation heterozygote carrying an additional tertiarychromosome for those chromosomes involved inthe translocation (2n(TAL.BL) + AS.BS).

From within the above 10 types, 4 types namely pri-mary, secondary, tertiary and telo trisomics have beenrecovered in a number of species and studied in detail(Khush, 1973).

II. Two chromosome additions.These aneuploidscarry two chromosomes in addition to the standardcomplement.1. Double trisomic dTri: An individual trisomic for

two different chromosomes of the standard com-plement (2n + AS.AL + DS.DL).

2. Diacrotrisomic DaTri: An aneuploid carrying twohomologous acrocentric chromosomes [result ofbreak(s) at the end(s)] besides the standard com-plement. The aneuploid is partial tetrasomic for

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a part of one of the chromosomes of the standardcomplement (2n + 2 acro DSDL).

3. Tetrasomic T: An individual having an extra pairof homologous chromosomes from the standardcomplement [2n + 2 (AS.AL)].

4. Monotertiary tetrasomic MteT: An individual hav-ing a normal and a tertiary chromosome in addi-tion to the standard complement (2n + AS.AL +BS.AL).

5. Ditertiary tetrasomic DteT: An individual havingtwo additional homologous tertiary chromosomes[2n + 2(BS.AL)].

6. Ditelotetrasomic DtT: An individual having anadditional pair of homologous telocentric chromo-somes [2n + 2(.DL)].

7. Inversion telotetrasomic ItT: The aneuploid is pri-mary trisomic and inversion telotrisomic for thesame chromosome (2n + DS.DL + .DSDL).

8. Inversion ditelotetrasomic IDtT: An individualhaving an extra pair of homologous telocentricchromosomes; the telocentrics being the resultof pericentric inversion and misdivision [2n +2(.DSDL)].

9. Inversion telotrisomic plus primary trisomic ItTripTri: An aneuploid primary trisomic for one chro-mosome and inversion telotrisomic for anotherchromosome of the complement (2n + AS.AL +.DSDL).

III. Three or more chromosome additions.Theseaneuploids carry three or more chromosomes in ad-dition to the basic complement.1. Triple trisomic (trp)Tri: An individual trisomic

for three different chromosomes of the standardcomplement (2n + AS.AL + BS.BL + DS.DL).

2. Tetra trisomic (tet)Tri: An individual which istetrasomic for one chromosome and trisomic for adifferent chromosome [2n + AS.AL + 2(DS.DL)].

3. Inversion ditelotetrasomic plus primary trisomicIDtT pTri: A primary trisomic carrying in addi-tion two telocentric chromosomes [2n + AS.AL +2(.DSDL)].

4. Pentasomic P: An individual carrying three homol-ogous chromosomes in addition to the standardcomplement so that this chromosome is repre-sented five times [2n + 3(DS.DL)].

5. Inversion tritelopentasomic ItP: An individual hav-ing three additional homologous telocentric chro-mosomes. The aneuploid is pentasomic for somesegments [2n + 3(.DSDL)].

6. Inversion tritelopentasomic plus trisomic ItPTri: Aprimary trisomic that has in addition three homol-ogous telocentric chromosomes [2n + AS.AL +3(.DSDL)].

7. Quadruple trisomic QTri: An aneuploid, trisomicfor four different chromosomes of the standardcomplement [2n + AS.AL + BS.BL + CS.CL +DS.DL).

8. Hexasomic H: Aneuploid in which one chromo-some of the complement is represented six times[2n + 4(DS.DL)].

9. Inversion tetratelo hexasomic ItH: An individ-ual having four additional homologous telocen-tric chromosomes. The aneuploid is as a resulthexasomic for some segments [2n + 4(.DSDL)].

10. Octosomic O: Aneuploid in which one chromo-some is represented eight times [2n + 6(AS.AL)].

This category of aneuploids is the least studied. Meio-sis of these aneuploids is characterized by associationswhich reflect their chromosome constitution (Table 1).

B. Compensation aneuploids

This category comprises aneuploids in which loss ofa chromosome of the standard complement is com-pensated by presence of more than one altered chro-mosomes, leading to increase in the number of chro-mosomes or chromosome segments. This class ofaneuploids includes following types.1. Telo-iso compensating trisomic tiCTri: A trisomic

with the missing chromosome compensated for byone iso- and one telocentric chromosome (2n –AS.AL + AS.AS + .AL).

2. Telo-tertiary compensating trisomic tteCTri: Acompensating trisomic with the missing chromo-some compensated for by one telocentric andone tertiary chromosome (2n – AS.AL + .AS +BS.AL).

3. Diiso compensating trisomic DiCTri: A trisomicfrom which one chromosome is missing but itsloss is compensated by two isochromosomes, onefor each arm of the missing chromosome (2n –DS.DL + DS.DS + DL.DL).

4. Ditertiary compensating trisomic DteCTri: A tri-somic in which the missing chromosome is com-pensated for by two tertiary chromosomes, onehaving long and the other short arm of the missingchromosome (2n – AS.AL + AS.BL + BS.AL).

5. Iso-tertiary compensating trisomic iteCTri: A tri-somic in which the missing chromosome is com-

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pensated for by one iso- and one tertiary chromo-some (2n – AS.AL + AS.AS + BS.AL).

6. Double telotrisomic plus primary trisomic dtTripTri: An individual trisomic for one chromosome,monosomic for the other, and carrying in additiontwo telocentrics one for each arm of the missingchromosome (2n – AS.AL + .AS + .AL + DS.DL).

7. Double telotrisomic plus tertiary trisomic dtTriteTri: An individual monosomic for one chromo-some and having instead a tertiary chromosomeand two telocentrics. The latter compensate forthe missing chromosome of the basic complement(2n – AS.AL + .AS + .AL + BS.DL).

8. Ditelo diiso tetrasomic DtDiT: An individual inwhich the loss of two chromosomes is compen-sated by two telocentrics and two isochromosomes[2n – 2(AS.AL) + 2(.AL) + 2(AS.AS)].

9. Dimonotelo tetrasomic DMtT: A monosomic withthe missing chromosome compensated for by threetelocentrics, two for one arm and one for thesecond arm of the missing chromosome [2n –AS.AL + 2(.AS) + .AL)].

10. Dimonotelo tetrasomic plus primary trisomicDMtT pTri: This individual is primary trisomic forone chromosome, deficient for the other chromo-some and has in addition three telocentrics, twofor one and one for the other arm of the miss-ing chromosome [2n – AS.AL + 2(.AS) + .AL +DS.DL].

11. Dimonotelo tetrasomic plus double telotrisomicDMtT dtTri: An individual deficient for two non-homologous chromosomes, having instead five te-locentrics, two representing an arm of one missingchromosome and the other three compensating forthe three other missing arms (two of one and thethird of the second chromosome) [2n – AS.AL –BS.BL + 2(.AS) + .AL + .BS + .BL)].

12. Double ditelopentasomic dDtP: A monosomic inwhich the missing chromosome is compensated byfour telocentrics, two for each arm [2n – AS.AL +2(.AS) + 2(.AL)].

C. Deletion aneuploids

This category includes aneuploids deficient for one ormore chromosomes or chromosome segments. Theyare of the following types.1. Monosomic M: Aneuploids deficient in one chro-

mosome of the standard complement (2n –DS.DL).

2. Tertiary monosomic teM: Aneuploids in whichthe arms of two nonhomologous chromosomes aremissing and the remaining two arms have joinedforming a tertiary chromosome (2n – AS.BL).

3. Monotelodisomic MtD: Aneuploids deficient inone chromosome arm (2n – .AS).

4. Monotelosomic Mt: Aneuploids missing one fullchromosome and one arm of the other homologue[2n – 2(AS.AL) + .AS].

5. Ditelosomic Dt: An individual missing two homol-ogous arms [2n – 2(AS.AL) + 2(.AS)].

6. Double monotelosomic dMt: A nullisomic withtwo telocentrics representing two arms of onechromosome of the missing pair [2n – 2(AS.AL) +.AS + .AL)].

7. Monotelo monoisosomic MtMi: A nullisomic inwhich one arm of the missing pair is representedby a telocentric and the other arm by an isochro-mosome [2n – 2(AS.AL) + AS.AS + .AL)].

8. Monoisosomic Mi: A nullisomic in which one armof the missing pair is represented as an isochromo-some [2n – 2(AS.AL) + AS.AS)].

9. Ditelo monotelosomic DtMt: An individual fromwhich one chromosome pair is missing but threetelocentrics, two for one arm and one for anotherarm of the missing chromosome are present [2n –2(AS.AL) + .AS +2(.AL)].

10. Nullisomic N: Aneuploids deficient for one ho-mologous chromosome pair [2n – 2(AS.AL)].

11. Double monosomic dM: Aneuploids deficient fortwo non-homologous chromosomes (2n - AS.AL– BS.BL).

12. Triple monosomic (trp)M: Individuals from whichthree different chromosomes are missing (2n –AS.AL – BS.BL – CS.CL).

13. Double nullisomic dN: An individual from whichtwo pairs of chromosomes are missing [2n –2(AS.AL) – 2(BS.BL)].

From the aneuploids listed above monosomics andnullisomics have been raised and utilized extensivelyin several crop plants especially wheat, oats, andcotton (Burnham, 1962; Khush, 1973).

D. Two-in-one aneuploids

These individuals represent addition aneuploids forsome chromosome (s)/chromosome part(s) and dele-tion aneuploids for other chromosome(s)/chromosomepart(s) of the standard set. In these aneuploids the stan-dard complement is not complete. The following typesare referred to this category.

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Table 2. Cytological characteristics of various types of aneuploids

Aneuploid Reference Plant species Characteristic meiotic

configuration

A. Addition aneuploids

I. Single chromosome additions

1. pTri Goodspeed & Avery, 1939 Nicotiana sylvestris (n-1) II + 1III

2. sTri Goodspeed & Avery, 1939 Nicotiana sylvestris (n-1) II + 1III

3. teTri Goodspeed & Avery, 1939 Nicotiana sylvestris (n-2) II + 1V

4. tTri Khush & Rick, 1968 Lycopersicon esculentum (n-1) II + 1III

5. ItTri Dhar et al., 1990; Dhar 1991 Plantago lagopus (n-1) II + 1III

6. mTri Fujigaki & Tsuchiya, 1981 Hordeum vulgare (n-1) II + 1III

7. aTri Tsuchiya & Fujigaki, 1981 Hordeum vulgare (n-1) II + 1III

8. (I) pTri Burnham, 1930 Zea mays (n-2) II + 1V

9. (I)sTri Rao et al., 1988 Pennisetum americanum (n-2) II + 1V

10. (I)teTri Rao et al., 1988 Pennisetum americanum (n-2) II + 1V

II Two chromosome additions

1. dTri Frost, 1927 Matthiola incana (n-2) II + 2III

2. DaTri Shahla & Tsuchiya, 1986 Hordeum vulgare (n-1) II + 1IV

3. T Blakeslee, 1921 Datura stramonium (n-2) II + 1IV

4. MteT Gill, 1974 Lycopersicon esculentum (n-2) II + 1VI

5. DteT Gill, 1974 Lycopersicon esculentum (n + 1) II

6. DtT Fedak & Helgason, 1970 Hordeum vulgare (n + 1) II

7. ItT Dhar, unpublished Plantago lagopus (n-1) II + 1IV

8. IDtT Dhar & Koul, 1995 Plantago lagopus (n + 1) II

9. ItTripTri Dhar, unpublished Plantago lagopus (n-2) II + 2III

III. Three or more chromosome additions

1. (trp) Tri Lesley, 1928 Lycopersicon esculentum (n-3) II + 3III

2. (tet) Tri Sai Kumar et al., 1982 Pennisetum americanum (n-2) II + 1III + 1IV

3. IDtTpTri Dhar, unpublished Plantago lagopus (n) II + 1III

4. P Sapre & Barve, 1983 Coix gigantea (n-1) II + 1V

5. ItP Dhar & Koul, 1995 Plantago lagopus (n) II + 1III

6. ItPTri Dhar, unpublished Plantago lagopus (n-1) II + 2III

7. QTri Sapre & Mishra, 1990 Coix lacryma-jobi (n) III

8. H Sapre & Barve, 1983 Coix gigantea (n-1) II + 1VI

9. ItH Dhar & Koul, 1995 Plantago lagopus (n) II + 1IV

10. O Sapre & Naik, 1991 Coix gigantea (n-1) II + 1VIII

B. Compensation aneuploids

Compensating trisomic CTri Khush & Rick, 1967 Lycopersicon esculentum (n-2) II + 1V

1. tiCTri Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 1III

2. tteCTri Khush, 1973 Triticum spp. (Triticinae) (n-2) II + 1V

3. DiCTri Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 1III

4. DteCTri Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-2) II + 1V

5. iteCTri Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-2) II + 1V

6. dtTripTri Pantulu & Rao, 1981 Pennisetum americanum (n-2) II + 2III

7. dtTriteTri Pantulu & Rao, 1981 Pennisetum americanum (n-3) II + 1III + 1V

8. DtDiT Kamanoi, 1973 Secale cereale (n + 1) II

9. DMtT Pantulu & Rao, 1981 Pennisetum americanum (n-1) II + 1IV

10. DMtTpTri Pantulu & Rao, 1981 Pennisetum americanum (n-2) II + 1III + 1IV

11. DMtTdtTri Pantulu & Rao, 1981 Pennisetum americanum (n-2) II + 1III + 1IV

12. dDtP Pantulu & Rao, 1981 Pennisetum americanum (n-1) II + 1V

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Table 2. (Continued)

Aneuploid Reference Plant species Characteristic meioticconfiguration

C. Deletion aneuploids1. M Clausen & Goodspeed, 1926 Nicotiana tabacum (n-1) II + I2. teM Rick, 1943 Petuniaspp. (n-2) II + 1III3. MtD Kimber & Sears, 1968 Triticum spp. (Triticinae) (n) II4. Mt Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + I5. Dt Kimber & Sears, 1968 Triticum spp. (Triticinae) (n) II6. dMt Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 2I7. MtMi Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 2I8. Mi Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + I9. DtMt Kimber & Sears, 1968 Triticum spp. (Triticinae) (n) II + I

10. N Sears, 1941 Triticum spp. (Triticinae) (n-1) II11. dM Khush, 1973 Triticum spp. (Triticinae) (n-2) II + 2I12. (trp) M Khush, 1973 Triticum spp. (Triticinae) (n-3) II + 3I13. dN Sapre & Barve, 1984 Coix gigantea (n-2) IID. Two-in-one aneuploids1. MTri Barve & Sapre, 1986 Coix gigantea (n-2) II + I + 1III2. tiD Kimber & Sears, 1968 Triticum spp. (Triticinae) (n) II3. MiD Kimber & Sears, 1968 Triticum spp. (Triticinae) (n) II4. Di Kimber & Sears, 1968 Triticum spp. (Triticinae) (n) II5. DtTri Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 1III6. tiTri Khush, 1973 Triticum spp. (Triticinae) (n-1) II + 1III7. DiTri Kimber & Sears, 1968 Triticum spp. (Triticinae) (n) II + 1I8. Trit Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 1III9. Trii Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 1III

10. dMtTri Pantulu & Rao, 1981 Pennisetum americanum (n-2) II + 2III11. MtTridtTri Pantulu & Rao, 1981 Pennisetum americanum (n-2) II + 2III12. NTri Matsumura, 1954 Triticum spp. (n-2) II + 1III13. NT Sears, 1966 Triticum aestivum (n-2) II + 1IVE. Pseudo-aneuploids1. dMi Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 2I2. dtTri Kimber & Sears, 1968 Triticum spp. (Triticinae) (n-1) II + 1III3. dtTri(I) Pantulu & Rao, 1981 Pennisetum americanum (n-3) II + 1III + 1IV4. dDt Pantulu & Rao, 1981 Pennisetum americanum (n+1) II5. ddtTri Pantulu & Rao, 1981 Pennisetum americanum (n-2) II + 2III6. dDtdtTri Pantulu & Rao, 1981 Pennisetum americanum (n) II + 1III

1. Mono-trisomic MTri: A typical two-in-one aneu-ploid which is monosomic for one and trisomicfor another chromosome of the complement (2n –AS.AL + DS.DL).

2. Teloisodisomic tiD: An individual with one chro-mosome pair missing but having a telocentric andan isochromosome for one arm of the two missingchromosomes [2n – 2(AS.AL) + .AS + AS.AS].

3. Mono-isodisomic MiD: An individual deficient forone chromosome and having an isochromosomefor one arm of the missing chromosome (2n –AS.AL + AS.AS).

4. Diisosomic Di: A nullisomic having two ho-mologous isochromosomes for the same arm ofthe missing chromosome pair [2n – 2(DS.DL) +2(DL.DL)].

5. Ditelotrisomic DtTri: A monosomic having a pairof homologous telocentric chromosomes for onearm of the missing chromosome [2n – DS.DL +2(.DL)].

6. Teloisotrisomic tiTri: An individual deficient forone chromosome and carrying instead a telocen-tric and an isochromosome for the same arm ofthe missing chromosome (2n – DS.DL + DL.DL +.DL).

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Table 3. Proposed new names of some of the aneuploids

Previous name Chromosomal formula Proposed name

1. Double telotrisomic 2n-AS.AL + .AS + .AL Mono double telo

plus primary trisomic + DS.DL disomic plus primary

dtTripTri trisomic MdtDpTri

2. Double telotrisomic 2n-AS.AL + .AS + .AL Mono double telodisomic

plus tertiary trisomic + BS.DL plus tertiary

dtTriteTri trisomic MdtDteTri

3. Dimonotelo tetrasomic 2n-AS.AL +2(.AS) + .AL Mono ditelo telo-

DMtT trisomic MDttTri

4. Dimonotelo tetrasomic 2n-AS.AL-BS.BL + 2(.AS) Nulli ditelo telo

plus double telo- + .AL + .BS +.BL trisomic plus

trisomic DMtTdtTri double telodisomic

NDttTridtD

5. Double ditelopenta- 2n-AS.AL + 2(.AS) + 2(.AL) Mono double ditelo-

somic dDtP trisomic MdDtTri

6. Monotelodisomic MtD 2n-.AS Monotelosomic Mt

7. Monotelosomic Mt 2n- 2(AS.AL) + .AS Nullitelosomic Nt

8. Ditelosomic Dt 2n-2(AS.AL) + 2(.AS) Nulli ditelosomic NDt

9. Monoisosomic Mi 2n-2(AS.AL) + AS.AS Nulli isosomic Ni

10. Monotelo monoiso- 2n-2(AS.AL) + AS.AS + .AL Nulli teloisosomic

somic MtMi Nti

11. Double monotelo- 2n-2(AS.AL) + .AS + .AL Nulli double telo

somic dMt somic Ndt

12. Ditelo monotelosomic DtMt 2n-2(AS.AL) + 2(.AS) + .AL Nulli tritelosomic NTrit

13. Diisosomic Di 2n-2(AS.AL) + 2(AS.AS) Nulli diisosomic NDi

14. Telo-isodisomic tiD 2n-2(AS.AL) + .AS + AS.AS Nulli telo-iso disomic NtiD

15. Ditelotrisomic DtTri 2n-DS.DL + 2(.DL) Mono ditelodisomic MDtD

16. Diisotrisomic DiTri 2n-DS.DL + 2(DL.DL) Mono diiso disomic MDiD

17. Teloisotrisomic tiTri 2n-AS.AL + .AS + AS.AS Mono telo isodisomic MtiD

18. Tritelosomic Trit 2n-2(DS.DL) + 3(.DL) Nulli tritelodisomic NTritD

19. Triisosomic Trii 2n-2(DS.DL) + 3(DL.DL) Nulli triisodisomic NTriiD

20. Double monotelo 2n-AS.AL-BS.BL + 2(.AL) Double mono double

trisomic dMtTri + 2(.BL) ditelo disomic dMdDtD

21. Monotelotrisomic plus 2n-AS.AL-BS.BL + 2(.AL) Double mono tetra

double telotrisomic MtTridtTri + .BS + .BL telo trisomic dM(tet)tTri

22. Double monoisosomic 2n-2(DS.DL) + DS.DS Nulli double iso

dMi + DL.DL disomic NdiD

23. Double telotrisomic 2n-AS.AL + .AS + .AL Mono double telo

dtTri disomic MdtD

24. Double telotrisomic 2n(TBL.DL)-AS.AL Mono double telodisomic

plus interchange dtTri(I) + .AS + .AL plus interchange MdtD(I)

25. Double ditelosomic dDt 2n-2(AS.AL) + 2(.AS) Nulli double ditelo

+ 2 (.AL) disomic NdDtD

26. Double double telo- 2n-AS.AL-BS.BL + .AS + Double mono tetra

trisomic ddtTri + .AL + .BS + .BL telodisomic dM(tet)tD

27. Double ditelosomic plus 2n-2(AS.AL)-DS.DL + Nulli mono double

double telotrisomic dDtdtTri 2(.AS) + 2(.AL) + .DS + .DL ditelodisomic NMdDtD

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7. Diisotrisomic DiTri: A monosomic having in placeof the missing chromosome a pair of homolo-gous isochromosomes for one arm of the missingchromosome [2n – DS.DL + 2(DL.DL)].

8. Tritelosomic Trit: An individual missing one chro-mosome pair but having three homologous telo-centric chromosomes for one arm of the missingpair [2n – 2(DS.DL) + 3(.DL)].

9. Triisosomic Trii: An individual deficient for achromosome pair and having instead three ho-mologous isochromosomes for one arm of thetwo missing chromosomes [2n – 2(DS.DL) + 3(DL.DL)].

10. Double monotelotrisomic dMtTri: An individualmissing two non-homologous chromosomes buthaving instead four telocentrics; two for an arm ofone chromosome and two for an arm of the othermissing chromosome [2n – AS.AL – BS.BL +2(.AL) + 2(.BL)].

11. Monotelotrisomic plus double telotrisomic Mt-Tri dtTri: An individual deficient in two differentchromosomes, but having four telocentrics; twoof which represent an arm of one missing chro-mosome and one each representing the two armsof another missing chromosome [2n – AS.AL –BS.BL + 2(.AL) + .BS + .BL)].

12. Nulli-trisomic NTri: Aneuploids trisomic for onechromosome and nullisomic for another [2n –2(DS.DL) + AS.AL].

13. Nulli-tetrasomic NT: Aneuploids nullisomic forone chromosome and tetrasomic for another [2n –2(DS.DL) + 2(AS.AL)].

E. Pseudo-aneuploids

This category includes chromosome variants whichdo not represent true aneuploids. They may not havealtered chromosome numbers. Even when their chro-mosome number is altered the gene content is the sameas in disomics. They have been named substitutiondiploids by Sybenga (1975). To this category belongthe following types of aneuploids.1. Double monoisosomic dMi: An individual de-

ficient for a chromosome pair and having in-stead two isochromosomes, one for each arm ofthe missing chromosome pair [2n – 2(DS.DL) +DS.DS + DL.DL].

2. Double telotrisomic dtTri: A monosomic withthe missing chromosome represented by two telo-centrics, one for each arm of the missing chromo-some (2n – AS.AL + .AS + .AL).

3. Double telotrisomic plus interchange dtTri(I): Adouble telotrisomic in which two other chromo-somes are involved in a reciprocal translocation[2n(TBL.DL) – AS.AL + .AS + .AL].

4. Double ditelosomic dDt: An individual deficientfor a pair of homologous chromosomes but havinginstead four telocentric chromosomes one for eachmissing arm [2n – 2(AS.AL) + 2(.AS) + 2(.AL)].

5. Double double telotrisomic ddtTri: A doublemonosomic in which each missing arm is repre-sented by a telocentric chromosome [2n – AS.AL– BS.BL + .AS + .AL + .BS + .BL].

6. Double ditelosomic plus double telotrisomic dDtdtTri: An individual nullisomic for one chromo-some, monosomic for another and having insteadsix telocentrics, each telocentric representing amissing arm [2n – 2(AS.AL) – DS.DL + 2(.AS) +2(.AL) + .DS + .DL].

All the types of aneuploids can be identified duringmeiosis. Table 2 lists the aneuploids, the plants inwhich they were first reported and the characteristicmeiotic configurations by which they can be identified.

In categorizing the aneuploid types emphasis hasbeen laid on changes in the gene content because ofaneuploidy. Some terms listed above, which have beencoined by earlier workers, on the basis of changes inchromosome number, have become ambiguous and donot convey the precise nature of the aneuploid. Suchnames have been substituted by new names (see Ta-ble 3). The first word of these names designates themagnitude of deletion, the second word refers to thesubstitution and the third to the overall status of theindividual.

Acknowledgements

The authors thank the Head, Department of Bio-sciences, University of Jammu for providing neces-sary facilities. We are grateful to Dr. J.L. Karihaloo,NBPGR, IARI New Delhi, for making valuable sug-gestions. We are also thankful to the reviewers for crit-ical evaluation and suggestions for the improvement ofthe paper.

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