Question

Poodle breeders have selectively bred poodles in three sizes. Standard poodles are about 22 inches at the shoulder, miniature poodles are approximately 14 inches, and toy poodles are less than 10 inches. Suppose that you begin with a miniature poodle and want to breed a new type of toy poodle. The original population of miniature poodles has a mean height of 14 inches, but the dogs chosen to produce the next generation of poodles has a mean height of only 12 inches. The next generation of dogs has a mean height of 12.4 inches.

Calculate the selection differential, S, for poodle size.

Calculate the response to selection, R, for poodle size.

Calculate the narrow‐sense heritability, h2, for poodle size.

Assuming that S, R, and h2 remain constant, determine the minimum number of generations it will take to produce a new breed of toy poodles: 2,4,5, or 3 generations?

Answer 1

Given:

Size of Standard poodles = 22 inches
Size of Miniature poodles = 14 inches
Toy poodles = 10 inches

Size of original population (Miniature poodles) = 14 inches
Size of dogs selected for breeding = 12 inches
Size of progeny generation = 12.4 inches

Therefore;

Selection Differential (S)
= Size of dogs selected for breeding - Size of original population = 12 inches - 14 inches = - 2 inches

Selection Response (R)
= Size of dogs in progeny population - Size of original population = 12.4 inches - 14 inches = - 1.6 inches

Narrow Sense Heritability = h2 = R/S = - 1.6/-2 = 0.8

So,

h2 = 0.8 ; S = -2 ; R = -1.6

In the next generation;

h2 = R/S

=> 0.8 = (Size of Generation 2 - Size of Generation 1)/(-2)
=> 0.8 * (-2) = Size of Generation 2 - 12.4 inches
=> - 1.6 = Size of generation 2 - 12.4 inches
=> Size of generation 2 = 12.4 inches - 1.6 inches
=> Size of generation 2 = 10.8 inches

So, from generation 0 to generation 1, the size decreased from 14 inches to 12.4 inches. From generation 1 to generation 2, the size decreased from 12.4 inches to 10.8 inches. Therefore, in order to get to Toy Poodles, we would need to selectively breed the dogs for 3 generations.