ANSC 4018 Notes

ANSC 4018 Notes - ANSC 4018 Notes: 1. Heritability (h^2): a...

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1. Heritability (h^2): a measure of the strength of the relationship between performance (phenotypic values) and breeding values for a trait in a population. 2. With high heritability, breeding values generally have a large influence on phenotypic values. 3. Positive breeding values tend to be associated with above average performance, negative breeding values tend to be associated with below average performance, and the larger breeding values (positive or negative), the larger the phenotypic deviations from the mean. 4. There is a strong relationship between breeding values and animal performance. 5. When heritability is high, performance is, on average, a good indicator of breeding value. 6. Animals with netter performance themselves typically have better breeding values and therefore produce better performing offspring. 7. Animals with poorer performance will typically have worse breeding values and produce poorer performance offspring. 8. Heritability is not the correlation between phenotypic values and breeding values; it is the square of the correlation between phenotypic values and breeding values: a. h^2= r^2(P,BV) 9. Heritability (in the broad sense, H^2): a measure of the strength of the relationship between performance (phenotypic values) and genotypic values for a trait in a population. a. H^2= r^2(P,G) 10. Broad sense heritability measures the total influence of genetics on the expression of a trait because it includes the contributions of both breeding value and gene combination value. 11. Because GCV cannot be inherited, broad sense heritability does not reflect the relationship between the performance of animals and their potential as parents. 12. Heritability can be thought of as the change in breeding value expected per unit change in phenotypic value. a. h^2= b(BV*P) 13. Heritability can also be thought of as a ratio of variances between BV and phenotypic values: a. h^2= σ^2(BV)/ σ^2(P) 14. Repeatability (r): a measure of the strength of the relationship between repeated records (repeated phenotypic values) for a trait in a population. 15. The first record on an animal is, on average, a good indicator of that animal’s second record. 16. A second definition of repeatability: a measure of strength (consistency, reliability) of the relationship between single performance records (phenotypic values) and producing abilities for a trait in a population. a. r = r(P1, P2) b. r = r^2(P,PA) 17. Repeatability ranges from -1 to +1. 18. Repeatability can be thought of as the change in producing ability expected per unit change in phenotypic value. a.
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ANSC 4018 Notes - ANSC 4018 Notes: 1. Heritability (h^2): a...

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