Reproductive Biology Cell Division –Somatic cell division (Mitosis) –Reproductive cell division (Meiosis) Flowering and Anthesis –Megagametogenesis (EMC.
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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)
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