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

Chromosome Numbers

Terminology

x = Number of chromosomes in a genome Genomic chromosome number

A set of different chromosomes“Oneness”

n = Number of chromosomes in gametesGametic chromosome number“Halfness”

    2n = Number of chromosomes in somatic cells

Somatic chromosome number“Wholeness”

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

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:

Life Cycle• Alternation of gametophytic (n) and sporophytic (2n) stages in a cycle

• Sporophytic (2n) stage is long and gametophytic (n) stage is brief

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)

Female (left) and Male (right) Flowers of Pumpkin

Confectionery Seed Pumpkin Production Near Hatton, ND

Honeybees

A Hermaphroditic Flower of Peony

Lady Slipper Orchid

Chasmogamous Flowers of Salpiglossis

Red, Delute Flower (RRdd)

Floral Parts

Influence of Pollination on Seed SetSalpiglossis sinuata

No. tetrads placed

Capsules setting seed (%)

Avg. no. of seeds per capsule

Avg. no. of seeds per tetrad

0 0 0 0

1 0 0 0

2 0 0 0

3 9.1 0.2 3.0

4 9.1 0.3 2.0

5 46.2 0.9 1.8

6 50.0 0.9 1.8

7 54.5 1.1 1.3

8 72.7 1.5 2.1

9 81.8 1.5 2.0

10 90.9 2.4 2.7

15 91.7 2.3 2.5

2. Hybridization

Inheritance of Flower Colorin Velvet Flower

(Salpiglossis sinuata)

RR or R- = Red flower color

rr = Yellow flower color

DD or D- = Solid color pattern

dd = Dilute color pattern

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

RRDD or R-D- (red, solid)

RRdd or R-dd (red, dilute)

rrDD or rrD- (yellow, solid)

rrdd (yellow, dilute)