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Plant Breeding

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Reproduction

Definition

Sequence of events involved in themultiplication & perpetuation of cells and

organisms. Types

Sexual - the increase of plants through seedformed from the union of male and female

gametesAsexual - the increase of plants through ordinary

cell division and differentiation

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Genetics

Basics of heredity

Gregor Mendel

1860s: traits

controlled by genes Qualtitative traits

single gene

Quantative traits

multiple genes Genome

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Genetics

Basics of heredity

Chromosome - structural units in the nucleuswhich carry the genes in linear order Made of DNA - deoxyribonucleic acid

Gene - the unit of inheritance determines the sequence of a given protein

Protein made by reading RNA - ribonucleic acid

messenger - mRNA

transfer - tRNA

ribosomal - rRNA

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8/6/2019 Plant Breeding Revised

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Genetics

Definitions

Allele alternate form of gene

Homozygous Alleles for trait are identical

Heterozygous Alleles for trait are not

identical

Genotype Organisms genetic

constitution Phenotype - Outward expression of the

genotype

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Genetics

Definitions

Dominant gene - When genes areheterozygous for a certain trait, one isexpressed

Recessive gene - When genes areheterozygous for a certain trait, one is notexpressed

Complete dominance: the dominant gene isthe only one expressed

Incomplete dominance: both genes play intothe phenotype, intermediate phenotype

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8/6/2019 Plant Breeding Revised

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Given: A= Red flowers; a= White flowers

Complete Dominance

Parents: AA x aa

Genotypic

Ratio

Aa- All

Phenotypic Ratio

Red- All

Parents: Aa x Aa

Genotypic RatioAA- 1

Aa- 2

aa- 1

PhenotypicR

atioRed- 3

White- 1

Parents: Aa x aa

Genotypic

Ratio

Aa- 2= 1

aa- 2= 1

Phenotypic Ratio

Red- 1

White- 1

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Given: AA= Red flowers; Aa= Pink flowers; aa= White flowers

Incomplete Dominance

Parents: AA x aa

Genotypic Ratio

Aa- All

Phenotypic Ratio

Pink- All

Parents: Aa x Aa

Genotypic

Ratio

AA- 1

Aa- 2

aa- 1

Phenotypic Ratio

Red- 1

Pink- 2

White- 1

Parents: Aa x aa

Genotypic Ratio

Aa- 2= 1

aa- 2= 1

Phenotypic Ratio

Pink- 1

White- 1

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Types of cell division

Mitosis

One cell divides into two cells and those two

daughter cells will each have bothchromosomes

Meiosis

One cell divides into two cells that both have

the full set. Then, each daughter cell willsplit into two cells, which will only have half

of the chromosome pair.

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Definitions

Gamete - Sex cell or nuclei (egg cell or sperm nuclei)produced during meiosis

Self pollination - Transfer of pollen from the male

structure to the female structure of a flower on the

same plant Cross pollination - Transfer of pollen between flowers

on different plants (plants must differ genetically)

Fertilization - The actual union of male and female

gametes Hybrid - The first generation offspring of a cross

between two individuals differing on one or more

genes

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Crop Improvement: Objective

To improve a certain trait in a species or toincorporate into or delete from a species acertain trait Increased productivity

Increased quality Ability to improve crop based on two

assumptions: Genetic variations exists

Adapted cultivars, breeder stock, wild plants,mutations, previously crossed plants, andintroductions from other parts of the world

Techniques exist for getting a favorablecombination of genes

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Methods with self-pollinating crops

Crops

Cotton, barley, sorghum, soybean, and

peanut

Crossing followed by selection

Pedigree Selection

Mass Selection

Backcross Method

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Methods with cross-pollinating crops

Crops

Alfalfa, corn, and fescue

Crossing followed by selection Pedigree selection

Mass selection

Backcross method Hybrid breeding

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Hybrid Production

Production of heterozygous populations

from the crossing of homozygous lines

Mostly used for cross-pollinated crops The hybrid seed must be reproduced each

year

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Hybrid Production

Steps involved

Produce inbred lines

Cross the inbred lines

Single cross hybrid

Harvest the female rows because they have the hybrid

seed

Double cross hybrid

Three way cross hybrid

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Weaknesses

Many years to provide a commercially

marketable seed.

Crossing can only occur within the same

species, and often selection is inefficientbecause it depends primarily on phenotypes.

Finding the desirable trait takes large numbers

of crosses so space can be a premium.