Chapter 9: Heritability & Repeatability

What has a heritability or repeatability?

a trait — NOT an individual

High heritability =

genes play more role, environment less role

Low heritability =

environment has big impact

GCV can be split into:

dominance and epistasis

New P =

BV + D + I + Ep + Et

I =

epistatic effects/interaction effect

Heritability is a ___ estimate:

population

Heritability =

relationship of difference in animal performance due to inheritance — varies from pop to pop and envi to envi

2 types of heritability:

H² and h²

H² stands for:

broad sense heritability

h² stands for:

narrow sense heritability

Broad SH =

measure of strength of a relationship between performance (P) and genotypic values (G) for a trait in a population

H² is denoted as:

H² = r²p,g

• square of the correlation between phenotypic values & genotypic values

BSH is only used in:

genetically identical individuals

What is not used in livestock and why?

BSH — there aren’t a lot of genetically identical individuals

Genetically identical =

same DNA — identical twins & clones

Narrow SH =

measure of strength of relationship between performance (P) and breeding value (BV) for a trait in a population

h² is denoted as:

h² = r²p,bv

• square of the correlation between phenotypic values and breeding value

Which type is used in humans?

BSH

Which type is used in animal populations?

NSH

What is the only type of heritability we talk about in this class?

NSH

Why is it narrow?

because it’s P to BV not P to G

Broad:

• includes BV plus GCV

• complete genotypic value

Narrow:

• only BV

• since GCV cannot be inherited

Range for h²:

• always positive

• 0-1

< 0.2 =

low

0.2-0.4 =

moderate

> 0.4 =

high

high h² means:

the parental performance is a good indicator of offspring performance (performance is close to BV)

low h² means:

the parental performance reveals little about offspring performance

(not much relationship between P & BV)

Polygenic traits cannot be:

100% heritable

What type of traits can be 100% heritable?

simply-inherited

h² = 0.7 means:

70% of variation in phenotype is due to BV

h² = 0.1 means:

BV only influences 10% of P

What are the 3 trait estimate categories?

1. Fitness

2. Production

3. Terminal

Fitness is:

fertility & survivability

Production examples:

milk production, growth rate, (anything associated with growth)

Terminal means:

end of life traits

Terminal trait examples:

carcass, skeletal, mature weights

h² of fitness is:

low

h² of production is:

moderate

h² of terminal is:

high

Fitness —> Production —> Terminal:

Young animals —> Growing animals —> Older animals

As age increases, environmental effect:

decreases

As age increases, NSH:

increases

As heritability gos us, environmental effects:

goes down

Alternative definition:

ratio of additive genetic variance (Va) to phenotypic variance (Vp)

h² =

Va/Vp OR Va/(Va+Vd+Vi+Vep+Vet)

High envi effect =

low h²

Low envi effect =

high h²

Objective =

choose individual with best BV

Phenotypic selection low h²:

• performance reveals little about BV

• genetic change is slow

Phenotypic selection high h²:

• performance is good indicator of BV

• genetic change is fast

What is very importance?

accuracy of records

Heritability is used in the prediction of:

BV, PD, PA

What does heritability indicate?

how conservative a prediction should be

Sow’s BV for # pigs weaned is:

very small

h² = 0.1

Dairy cow’s BV for % butterfat is:

high

h² = 0.55