Question

A horse breeder is interested in making genetic progress for racing the mile. She is evaluating two potential selection schemes. Data available for comparing each scheme includes a heritability of 0.30, a repeatability of 0.61, a phenotypic standard deviation of 2.5 seconds, and a phenotypic mean of 130 seconds. Females are selected in the top 70% of the population with an accuracy based on the average of 3 race records, and the generation interval for females is 5 years. The breeder is considering two alternative schemes for selecting males, and each of these schemes will include selecting males in the top 5% of the population.

i.Selection based on a single race record of the individual sire with an estimated generation interval of 6 years.

ii.Selection based on records of 5 progeny with 3 races each, and a generation interval of 10

years.

a)Compare each of these schemes and indicate which approach is the most optimal for maximizing

genetic progress.

Answer 1

The standard Formula as defined for genetic Progression is as Follows

R=S*h/L

Where

R = Response to Selection

S = Selection Differential ( Average genetic Values or the % of Population selected for breeding)

h = Heritability

L = Generation Interval between Parent and Offspring.

First lets see the genetic progress made in case of Female Population.

Substituting the values

S= .7 (70%)

h^2= .09 (.30 ^2)

L= 5 (years)

R = (.7 x .09) / 5

R= .126 Genetic Progression is Fixed for Female Popluation

Now for the Genetic Progression made in case of Male Population in case of Choice 1.

S= .05 (5 %)

h^2 = .09 (.30^2)

L= 6 (6 years)

Substituting the values

R = (.05 x .09) / 6

=. .075 is the Genetic Progression for Selection 1 for Males

Now for the Genetic Progression made in case of Male Population in case of Selection 2.

S= .05 (5 %)

h^2 = .09 (.30^2)

L= 10 (10 years)

Substituting the values

R = (.05 x .09) / 10

=. .045 is the Genetic Progression for Selection 2 for Males

Now coming to the maximising the genetic progression

1. Selecting the product between the Female Genetic Progression value of .126 and Male Selection 1 with Genetic Progression value of .075 Yields .00945
2. Selecting the product between the Female Genetic Progression value of .126 and Male Selection 2 with Genetic Progression value of .045 Yields .00567.

Hence comparing the 2 values of Genetic Progression Selection 1 maximises the genetic progression