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 reassortment 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 gametes
Gametic 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)
• Euploidy
Variation between chromosome sets
• Aneuploidy
Variation within a chromosome set
• Autoploidy
Multiplication 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
A diploid plant (2n=2x=14) would contain the following
chromosome numbers depending on aneuploidy
conditions:
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
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 Set
Salpiglossis 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 Color
in Velvet Flower
(Salpiglossis sinuata)
RR or Rrr
DD or Ddd
= Red flower color
= Yellow flower color
= Solid color pattern
= Dilute color pattern
P1
P2
x
Dilute Red
(RRdd)
Solid yellow
(rrDD)
F1
Solid Red
(RrDd)
F2
Solid red
(R-D-)
9
Dilute red
(R-dd)
3
Solid yellow
(rrD-)
Dilute yellow
(rrdd)
3
1
RRDD or R-D(red, solid)
RRdd or R-dd
(red, dilute)
rrDD or rrD(yellow, solid)
rrdd
(yellow, dilute)