breeding values and expected progeny differences Flashcards
what is a breeding value
-the number that represents the value as a parent
-the deviation of the animals progeny compared to the average reference population
what does the breeding value depend on
-the average performance of the reference population
-the value of the alleles that each progenitor can transfer to its progeny
what makes up the G in P=G+E
A(additive effect, breeding value)+D(dominance deviation)+I(gene interactions)
what is an animals breeding value directly proportional to
how many favourable alleles it carries AND transmits to offspring
genotypic values (V)
-two alleles, A1 and A2
-three genotypes:
-A1A1
-A1A2
-A2A2
how to alter phenotype
-impact environment
-change genotype
V
genotypic value (half the breeding value)
A
breeding value (additive genetic component
what happens if the A=0 or less
no improvement to the herd
how should the genotypic values of bulls be calculated based on
breeding bulls to a wide varity of cows, ideally in a wide variety of herds in many environments
dairy bull EPD scored require milk records form 50 daughters from several herds
what is the breeding value in relation to the average deviation
twice the average deviation of the animals offspring form mean
BV (A)= (equation)
2 x progeny difference
what is the breeding value a measure of
-the animals expected progeny perfromance relative to the population mean
-twice the average deveation of the animals offspring from the mean
-twice because only 1/2 is being measured form one parent
what is breeding value affected by
-gene frequency
-types of gene action (dom, codom)
-difference in genotypic value between the homozygotes
ie its not constant, gene frequency can only be altered through selection
-its not possible to determince an animals true breeding value but can estimate it. = estimated breeding value
things you need for calculations of EPDs
-animals own performance (important with highly heritable traits)
-pedigree
(sire and maternal grandsire (min), imprtant with traits of low heritability, used for young animals with young progeny
-progeny records
(important with traits of low heritability, important with traits that cant be measure in the individual)
what are EPDs derived from
-complex calculations to estimate the animals genetic worth as a parent
-they factor in many variables yp estimate only the genetic porportion that contributes towards the trait in the offspring
what is estimated breeding value
-genetic worth of an animal
how do you calculate estimated breeding value
-heritability x (individual - test average)
EPV vs EPD
-bull transmits 1/2 of his breeding value to his offspring dam transmits other half
-EPD is 1/2 of EBV
what does national (international) cattle evaluation by breed account for
-accounts for all pedigree relationships (parent, sib)
-accounts for herd location differences
-accounts for management differences
-accounts for relationships between traits
how often does nat (inter) cattle evaluations by breed recalculate EPDs
weekly, monthly, annually
what are some growth EPDs
birth weight, wean weight, yearling weight
what is accuracy for EPDs
-measure of reliability
-indicator of risk
-increase as more information is used to calculate EPD
combining molecular genomics with EPD
-predicts what it will be like based on genomics with out seeing results
-molecular genomics SNP chips
-it claims to improve accuracy in young sires
what does SNP stand for
single nucleotide polymorphism
