Selection differences and –intensity

Chapter 8: Selection response

Selection response

• Selection difference

• Selection intensity

• Selection respons

• Heritability of threshold traits

• Breeding value for threshold traits

• Genetic correlation

• Changes in correlated traits

S = PS - P

Selection difference, S

i = S/P

Selection intensity, i

Selection intensity table

Selection response, G individual selection

R = G = h2 S = h2 i P

= h i A

or

G = (IS – A)

Selection response, G

i = Selection intensity

rAI = Accuracy

A = Additiv genetic standard error

L = Generation interval

Extended formula for G general formula

Threshold traits

Heritability estimates for threshold traits

Threshold traitsscale problems

Threshold traitsDistribution of hip dysplasia (HD) in German Shepherd

dogsB1 and more normal, B2 and under HD

Threshold traits

Calculation of an index, I, for a threshold trait

Genetic correlation and change in secondary traits

• Pleiotropy

• Linkage

Example of negative genetic correlation

A1

A2

Determination of genetic correlation by selection

experiments

r Ax,Ay =Gy / Ay

Gx / Ax

Correlated change in trait y by selection for trait x

The genetic correlation is dynamic

Correlation between fitness and selected traits

Genetic correlation: Examples

Back lash on a genetic level -maximal fitness

Auto selection for litter size