Lecture_11_-_Heritability_and_Artificial_Selection_-_Ch_21-1

Lecture_11_-_Heritability_and_Artificial_Selection_-_Ch_21-1...

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Lecture 11 Lecture 11 Heritability and Artificial Heritability and Artificial Selection Selection (6 (6 th th Ed – Ch 21) Ed – Ch 21) (5 (5 th th Ed – Ch 6) Ed – Ch 6)
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Genetic Variation and Heritability Genetic Variation and Heritability If heritability of a particular trait is high, most of the differences among individuals for the trait in a population are due to genetic variation Selecting phenotypically superior animals for this trait has a much higher probability of passing that phenotypic superiority to their offspring
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Genetic Variation and Heritability Genetic Variation and Heritability On the other hand, if heritability of a particular trait is low, most of the differences among individuals for the trait in a population are due to environmental variation Selecting phenotypically superior animals for this trait doesn’t guarantee that the individuals with superior phenotypes will pass those phenotypes to their offspring
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Genetic Variation and Heritability Genetic Variation and Heritability In agriculturally important species, most of the economically important traits such as body weight gain, egg production, milk production, grain yield, etc. are quantitative in nature These traits are influenced by the genotypes of the individual animal or plant as well as the environmental conditions under which it exists Knowledge of the genetic variability and therefore the heritability of the trait allows us to develop selective breeding programs that optimize the genetic improvement and maximize the economic performance for the trait
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Genetic Variation and Heritability Genetic Variation and Heritability Other important traits such as reproductive performance and disease resistance also have important genetic components Understanding the genetic variability and heritability of these traits also helps us to develop selective breeding strategies to take advantage of the variability among individuals for these traits Many important medical traits of humans such as blood pressure and blood cholesterol levels are quantitative.
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Broad-Sense Heritability Broad-Sense Heritability Broad-sense heritability is the proportion of the total phenotypic variance that is due to genotypic variation in a population The symbol for broad-sense heritability is H 2 H 2 = V G / V P Range is from 0 to 1 H 2 represents all types of genetic variation such as variation due to the effects of individual alleles, variation due to the dominance relationships among alleles at a single locus and the variation due to the interaction of different alleles at different loci *** Some of this genetic variation can be passed on to the next generation and some of it cannot ***
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Narrow-Sense Heritability Narrow-Sense Heritability In addition to partitioning the total phenotypic variation into genetic and environmental components: V P = V G + V E We can also partition the genetic variation into three different genetic components: additive variation,
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