Chap 2. Biology of Propagation
1. General Terminology
a. 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
Tetraploid
Hexaploid
Octoploid
2x=24
4x=48
6x=72
8x=96
2n=24
2n=48
2n=72
2n=96
n=12
n=24
n=36
n=48
-----------------------------------------------------------------------------------------
Haploid
Triploid
Pentaploid
1x=12
3x=36
5x=60
2n=12
2n=36
2n=60
n= 6 (?)
n=18 (?)
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 reassortment 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 Polyploidy
Use 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)
• 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
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 chromosomes
b. 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 Pattern
Salpiglossis sinuata
RR or Rr
rr
DD or Dd
dd
Red flower color
Yellow flower color
Solid color pattern
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)
F1
Solid Red
(RrDd)
F2
Solid red
(R-D-)
9
Dilute red
(R-dd)
3
Solid yellow
(rrD-)
Dilute yellow
(rrdd)
3
1
2. Nomenclature
Based on ICBN (International Code of Botanical
Nomenclature)
a. Botanical Classification
Family-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 Blanc
Syringa 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
b. Uniform-
different characteristics
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