Question

: You start with a population of cattle in which the heritability of body weight is 0.7. You begin a program of artificial directional selection to increase body weight. You continue this generation after generation. What will happen to the frequencies of alleles of different genes that cause an increase in body weight, and the frequencies of those alleles that cause a decrease in body weight? What do you think will happen to the heritability of body weight after 20 generations of selection? Will it increase, decrease, or stay the same? Explain your reasoning. When will the population stop responding to selection?

Answer 1

Heritability accounts for the variance in trait due to genetic variants. Since for our character it is 0.7, this means genetic variants control the trait for 70 percent. Because we are selecting the trait of more body weight we are selecting alleles responsible for more body weight and hence they frequency of alleles responsible for more body weight will.increase. Nevertheless heritability will remain the same as still the variance due to non genetic factors haven't been altered as there is no change in the environment variable.

The population will stop responding to selection when the individual become pure for alleles responsible for more body weight.