Lecture 16 - Alleles And Inheritance (part 2)
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What are qualitative traits?
Traits that can be described but only measured subjectively • categories • coat color, horns (Controlled by a relative small number of genes; simply-inherited traits)
What are quantitative traits?
Numerically measured : continuous expression - milk yield, litter size, mature weight Controlled by many genes (polygenic)
What are the differences between qualitative and quantitative traits?
Quantitative - greater environmental influence, variable heritability Qualitative - less environmental influence, greater heritability
What is heritability?
Proportion of phenotypic variation that van be passed to next generation • measure of the strength of the relationship between phenotypes and breeding values • not constant; vary across populations and over time
How is heritability quantified?
A number between 0 and 1 (proportion) • low heritability = 0 - 0.2 (example reproductive traits) • moderate heritability = 0.2-0.4 (ex growth traits) • high heritability = 0.4-0.6 (ex carcass merit traits)
What is the influence of heritability on traits?
Low heritability -> no substantial change from generation to generation with selection High heritability -> greater degree of change (can be selected for superiority
What is genetic progress?
Selection differential x heritability
What is selection differential?
The phenotypic advantage of animals selected to be parents over the population average
What is the rate of genetic progress?
(Selection differential x heritability)/ generation interval
What is the generation interval
Average time required to replace one generation with the next
What are steps taken in mating systems to breed animals?
Selection : identify animals to breed Mating : determine which selected males will be bred to which selected females
What is random mating?
Selected animals mate at random • mating of selected animals is not controlled
What is inbreeding?
Mating of related animals (within a breed) • purebreds • to concentrate desired genes • creates inbreeding depression
What is line-breeding
• mating animals that have one common ancestor (Mild form of inbreeding)
What are some examples of line breeding and inbreeding?
Inbreeding : mating of sire to a daughter Line-breeding : mating of a grand sire to a granddaughter
What is outbreeding?
Mating of a relative that is not closely related • opposite of inbreeding • increase heterozygosity and decrease expression of deleterious recessive genes
What is heterosis?
Hybrid vigor - superiority of an out red animal • inversely related to heritability
What is breeding value?
Mating of individual with different but complementary breeding values