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Plant Breeding

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					Plant Breeding

Reproduction
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Definition
Sequence of events involved in the multiplication & perpetuation of cells and organisms.  Types
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Sexual - the increase of plants through seed formed from the union of male and female gametes  Asexual - the increase of plants through ordinary cell division and differentiation
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Genetics
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Basics of heredity
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Gregor Mendel – 1860s: traits controlled by genes
Qualtitative traits – single gene  Quantative traits – multiple genes  Genome
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Genetics
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Basics of heredity
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Chromosome - structural units in the nucleus which carry the genes in linear order
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Made of DNA - deoxyribonucleic acid determines the sequence of a given protein  Protein made by reading RNA - ribonucleic acid messenger - mRNA transfer - tRNA ribosomal - rRNA
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Gene - the unit of inheritance
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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 – Organism’s genetic constitution  Phenotype - Outward expression of the genotype
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Genetics
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Definitions
Dominant gene - When genes are heterozygous for a certain trait, one is expressed  Recessive gene - When genes are heterozygous for a certain trait, one is not expressed  Complete dominance: the dominant gene is the only one expressed  Incomplete dominance: both genes play into the phenotype, intermediate phenotype
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Complete Dominance
Given: A= Red flowers; a= White flowers Parents: AA x aa Genotypic Ratio Parents: Aa x Aa Genotypic Ratio AA- 1 Aa- 2 Phenotypic Ratio Red- All aa- 1 Parents: Aa x aa Genotypic Ratio

Aa- All

Aa- 2= 1
aa- 2= 1

Phenotypic Ratio
Red- 3 White- 1

Phenotypic Ratio Red- 1 White- 1

Incomplete Dominance
Given: AA= Red flowers; Aa= Pink flowers; aa= White flowers Parents: AA x aa Genotypic Ratio Aa- All Parents: Aa x Aa Genotypic Ratio Parents: Aa x aa Genotypic Ratio Aa- 2= 1 aa- 2= 1

AA- 1
Aa- 2

Phenotypic Ratio Pink- All

aa- 1 Phenotypic Ratio Phenotypic Ratio Pink- 1 White- 1

Red- 1
Pink- 2 White- 1

Types of cell division
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Mitosis
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One cell divides into two cells and those two daughter cells will each have both chromosomes
One cell divides into two cells that both have the full set. Then, each daughter cell will split into two cells, which will only have half of the chromosome pair.

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Meiosis
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Definitions
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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

Crop Improvement: Objective
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To improve a certain trait in a species or to incorporate into or delete from a species a certain trait
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Increased productivity Increased quality

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Ability to improve crop based on two assumptions:
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Genetic variations exists  Adapted cultivars, breeder stock, wild plants, mutations, previously crossed plants, and introductions from other parts of the world Techniques exist for getting a favorable combination of genes

Methods with self-pollinating crops
 Crops  Cotton, barley, sorghum, soybean, and peanut  Crossing followed  Pedigree Selection  Mass Selection  Backcross Method

by selection

Methods with cross-pollinating crops
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Crops
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Alfalfa, corn, and fescue

Crossing followed by selection
Pedigree selection  Mass selection  Backcross method
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Hybrid breeding

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
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Steps involved
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Produce inbred lines Cross the inbred lines
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Single cross hybrid
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Harvest the female rows because they have the hybrid seed

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Double cross hybrid Three way cross hybrid

Weaknesses
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Many years to provide a commercially marketable seed.  Crossing can only occur within the same species, and often selection is inefficient because it depends primarily on phenotypes.  Finding the desirable trait takes large numbers of crosses so space can be a premium.


				
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