Estimates of Breeding Values

Which part of the phenotype equation is transmittable from parent —> offspring

• P = A + D + I + E

A (additive genes) which is also breeding value (BV)

Why don’t parents transmit the same genes to all offspring?

Due to segregation during meiosis or Mendelian sampling

• So estimated BV (EBV) = ½ BV sire + ½ BV dam

Actual BV of an individual is not known so how can we gain information?

• From own performance

• Performance of its relatives

Why use information of relatives?

• Relatives have some genes in common

• Relatives are related by descent

What is progeny?

Parent-offspring relationship

Confidence in the estimate of BV increases when?

• By using the performance of its progeny and siblings

• More relatives are used in the BV estimate

• More relatives who are closely related to the individual are used in the BV estimate

Which type of relatives are appropriate in measuring BV in

• Traits which can be measured only in one sex

• Other traits

• Carcass traits

• Longevity or total lifetime productivity

Traits which can be measured only in one sex:

• Progeny

• Sibling

Other traits:

• Progeny

• Sibling

Carcass traits: Sibling

Longevity or total lifetime productivity:

• Progeny

• Sibling

What is the average effect of alleles (a)

How much an individual allele contributes to a trait on average in a population

What is the difference between genetic (phenotype) and breeding value (pass to offspring) and why?

Difference: Dominance deviation

Why: Offspring gain combination of alleles from both parents so it isn’t guaranteed that the same dominance interaction will occur

Dominance Deviation

• What is dominance deviation

• What does it mean where there’s no dominance

  • How does it affect breeding value predictions?

• What happens in incomplete dominance?

  • How does it affect breeding value predictions?

• What happens in complete dominance?

  • Why is it an issue for breeding value predictions?

What is dominance deviation: The difference between phenotype of a heterozygote and expected average of 2 homozygotes

What does it mean where there’s no dominance: Heterozygote lies exactly halfway between the 2 homozygotes, meaning there’s no dominance deviation

• How does it affect breeding value predictions: Means that BV is highly accurate because all genetic effects are additive and passed on predictably

What happens in incomplete dominance: Heterozygote’s phenotype is closer to one homozygote (not exactly in middle) so there’s some dominance deviation

• How does it affect breeding value predictions: Reduces accuracy of BV slightly as some of phenotype is due to non-additive effects (dominance)

What happens in complete dominance: Heterozygote has same phenotype as dominant homozygote, so large dominance deviation occurs

• Why is it an issue for breeding value predictions: Because dominance is not consistently inherited like additive effects

What is breeding value?

Sum of all average effects of alleles on all relevant traits of an individual as a parent

What is estimated transmitting ability?

½ of BV

Why could there be a difference in phenotype among offspring of the same family?

Due to

• Segregation and independent assortment of genes

• Environmental effect

Estimating Breeding Value with Sibling Info

• What happens to the accuracy of BV estimation as the number of sibs increases?

• Why does each additional sibling contribute less accuracy to BV estimation?

• For which traits is sibling information most useful?

  • Why

What happens to the accuracy of BV estimation as the number of sibs increases: Accuracy increases but each additional sibling contribute less than previous one

Why does each additional sibling contribute less accuracy to BV estimation: Because each new sibling adds less new data

For which traits is sibling info most useful: Traits with low heritability (fertility, disease resistance)

• Why: Siblings average out environmental effects