Chap 2 biology of propagation
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Chap 2. Biology of Propagation. 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

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Chap 2. Biology of Propagation

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Chap 2. Biology of Propagation

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

-----------------------------------------------------------------------------------------

Diploid2x=24 2n=24 n=12

Tetraploid4x=48 2n=48 n=24

Hexaploid6x=72 2n=72 n=36

Octoploid8x=96 2n=96 n=48

-----------------------------------------------------------------------------------------

Haploid1x=12 2n=12 n= 6 (?)

Triploid3x=36 2n=36 n=18 (?)

Pentaploid5x=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


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


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


AneuploidyVariation within a chromosome set

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)


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 PatternSalpiglossis sinuata

RR or RrRed flower color

rrYellow flower color

DD or DdSolid color pattern

ddDilute 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-)

3

Dilute yellow

(rrdd)

1


2. Nomenclature

Based onICBN (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:Syringavulgaris 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 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


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