Chap 2. Biology of Propagation

1. General Terminologya. Genotype: the genetic make-up of an organism

b. Phenotype: the external appearance of an organism (usually the outcome of interaction between a genotype and environment)

c. Ploidy: Variation in the genomic number (x) of chromosomes

x = genomic number of chromosomes

n = gametic number of chromosomes

2n = “wholeness”

n = “halfness”

Variation in Euploidy(for Organisms with x=12)

Ploidy No. Chromosomes Somatic Gametic-----------------------------------------------------------------------------------------

Diploid 2x=24 2n=24 n=12Tetraploid 4x=48 2n=48 n=24Hexaploid 6x=72 2n=72 n=36Octoploid 8x=96 2n=96 n=48-----------------------------------------------------------------------------------------

Haploid 1x=12 2n=12 n= 6 (?)

Triploid 3x=36 2n=36 n=18 (?)

Pentaploid 5x=60 2n=60 n=30 (?)-----------------------------------------------------------------------------------------

Seedless watermelons are triploids

Reproductive Biology

• Cell Division– Somatic cell division (Mitosis)– Reproductive cell division (Meiosis)

• Flowering and Anthesis – Megagametogenesis (EMC to Egg Cells)– Microgametogenesis (PMC to Pollen Grains)

• Pollination and Fertilization– Pollen germination on stigma– Pollen tube growth through style tissue– Double fertilization

Mitosis- Somatic Cell Division

- Ends up with same number of chromosomes in divided cells

- Divided cells are genetically identical to maternal cells

2N ---------► 2N + 2N

Meiosis• Reproductive cell division

• Undergoes 2 separate divisions

• Forms gametes

• Divided cells have a half of the chromosome numbers

• Ends up with genetic re-assortment by chromosomal translocation (cross-over)

2N ---►---► N + N + N + N

An Example of Meiosis

Fertility in Polyploid (Euploidy) Plants

Ploidy Somatic Gametic Fertility

Monoploid 2n=1x n = ? Very low

Diploid 2n=2x n = x High

Triploid 2n=3x n = ? Very low

Tetraploid 2n=4x n = 2x Variable

Pentaploid 2n=5x n = ? Variable

Hexaploid 2n=6x n = 3x Variable

Heptaploid 2n=7x n = ? Variable

Octoploid 2n=8x n = 4x Variable

Nonaploid 2n=9x n = ? Variable

Decaploid 2n=10x n = 5x Variable

Induction of PolyploidyUse Colchicine

Polyploidization• Use of Cholchicine to induce polyploids

• Colchicine interferes with spindle fiber function during metaphase of meiosis

Production of Seedless Watermelon

www.parkseed.com

Example of Ploidy Variation

Chromosome Number

Species Ploidy

Somatic

(2n)

Gametic

(n)

Genomic

(x)

Spinach 2x 12 6 6

Corn 2x 20 10 10

Potato 4x 48 24 12

Strawberry 8x 56 28 7

Polyploidy Terminology (continued)

• EuploidyVariation between chromosome sets

• AneuploidyVariation within a chromosome set

• AutoploidyMultiplication of the complete set of

genomes of a species• Alloploidy

Polyploid containing genetically different sets of chromosomes derived from 2 or more species

Aneuploidy Variation within a chromosome set

 

Aneuploidy

Somatic chromosome number  Examples

 Trisomic  2n + 1 (extra) 11  22  33  44  55  66 777

 Monosomic   2n - 1 (deficient) 11 22 3_ 44 55 66 77

 Double-trisomic 2n + 1 + 1 (2 extra) 11  22  33  44  555  66  777

4 of one chromosome 2n + 2 (2 extra) 11  22  33  44  5555  66  77

A diploid plant (2n=2x=14) would contain the following chromosome numbers depending on aneuploidy conditions:

Pollen Tetrad and Microgametophyte

  - One tube nucleus    - Two sperm nuclei 

Megagametophyte

  1 egg nucleus  2 polar nuclei  3 antipodal nuclei  2 synergids

   

Pollination and Fertilization, Angiosperms

Double Fertilization

A process of fertilization in which one male gamete (sperm nucleus, n) unites the egg nucleus (n) to form embryo (zygote, 2n) and the other sperm nucleus (n) unites polar nuclei (2n) to form endosperm (3n)

1. General Terminology (continued)a. Homozygous- Having like alleles at corresponding loci on

homologous chromosomesb. Heterozygous- Having unlike alleles at one or more

corresponding loci on homologous

c. Meiosis- Reproductive cell division (Reduction Division)- Chromosome number is reduced to one half- Results in formation of gametes (pollen, egg cells)- Allows genetic recombination

d. Mitosis- Somatic cell division- Chromosome number same in daughter cells- Results in somatic tissues genetically identical- Allows clonal duplication

Fruit Flesh Color and Skin Texture Inheritance - Peach

Inheritance of Flower Color and Color PatternSalpiglossis sinuata

RR or Rr Red flower color

rr Yellow flower color

DD or Dd Solid color pattern

dd Dilute color pattern

Gene Symbols

RR DD or R_R_ (red, solid)

RR dd or R_ dd (red, dilute)

rr DD or rrD_ (yellow, solid)

rr dd (yellow, dilute)

P1 P2

x

Dilute Red (RRdd)

Solid yellow (rrDD)

Solid Red (RrDd)

F1

Solid red (R-D-) 9

Dilute red (R-dd) 3

Solid yellow (rrD-) 3

Dilute yellow (rrdd) 1

F2

2. NomenclatureBased on ICBN (International Code of Botanical Nomenclature)

a. Botanical ClassificationFamily-Genus-Species-Variety-Form-

Individual -Subspecies - Clines- continuous variation - Ecotypes- discontinuous

variation

b. Cultivated Plants Genus, species, cultivar

Cultivar = Cultivated variety (cv.) Cultigen = Cultivated variety that has been naturalized

Examples: Syringa vulgaris cv. Mont BlancSyringa vulgaris ‘Mont Blanc’

3. Kinds of Cultivars a. Line- Self pollinated seed-propagated cultivar

(homozygous)- Inbred lines- Synthetic lines (composite lines)

b. Hybrids (sexual)F-1 hybrid- first generation progeny from a

cross between 2 inbred lines (single cross)

c. F-2 Cultivars (sexual) Cultivars made up of self-pollination of an F-1

3. Kinds of Cultivars (continued) d. Open Pollinated Cultivar (sexual)

- Cultivar made up of seeds formed by open pollination

- Can be mixtures of hybrids, selfs)

- Inbred lines

- Synthetic lines (composite lines)

e. Clonal Cultivars (asexual)

Clone- Plant propagated by asexual means

Asexual propagation- cuttings, tubers, bulbs, grafts, rhizomes, cormels, stolon

f. Apomictic Seeds (asexual) Seed formed from maternal (ovule) tissues

4. Requirements for New Cultivar a. Distinctive- Morphologically and physiologically

different characteristics b. Uniform- Homogeneity (Variation should be minimal)

Homogeneous (but, can be heterozygous as in F1)

Homozygous (no segregation)

c. Stable- A reasonable degree of reliability

Reproducible performance

d. Commercial- Must have agronomic or horticultural value