Phenotypic variation was analysed for milk production in a herd of dairy cattle
ID: 80919 • Letter: P
Question
Phenotypic variation was analysed for milk production in a herd of dairy cattle and the following variance components were obtained: Additive genetic variance (V_A) = 0.34 Environmental variance (V_E) = 0.69 Estimate the narrow-sense heritability of milk production. b. Joe is breeding cockroaches in his college room. He finds that the average wing length in his population is 2.5 cm. He chooses 4 male and 4 female cockroaches that have the largest wings with an average wing length of 4 cm. Joe interbreeds these. From earlier studies, he knows that the narrow-sense heritability for wing length in his population of cockroaches is 0.6. i) How much better are his breeding population (the selection differential) from the rest? ii) Do you expect the average EBV's of the male and female cockroaches to be the same? iii) What is the estimated breeding value (EBV) for these breeding cockroaches for wing length? iv) What should be the average wing length of the progeny of the selected cockroaches? v) would you expect the average wing length of the cockroaches to continue to increase over many years?Explanation / Answer
a)Phenotypic variance in a population is influenced by phenotypic variance and phenotypic variance.
Phenotypic variance (VP) = genetic variance (VG) + environmental sources (VE)
VP = VG + VE
Total amount of genetic variance = additive variance (VA) + dominance variance (VD) + and epistatic variance (VI)
(VG = VA + VD + VI)
Therefore Here, VP = VA + VE
VP = 0.34 + 0.69
= 1.03
Narrow sense heritablity of milk productionh2 = Additive genetic variance (VA) / Phenotypic variance (VP)
h2 =0.34 / 1.03
= 0.33 . ans.
b.
i) Here we need to calculate the selective differential and we will use this equation
S = 4 cm - 2.5 cm
= 1.5 cm
where S is the selection differential.
ii) yes... will be the same for both male and female and EBV is regardless of sex in this case.
iii) EBV calculation
Estimated Breeding Value = EBV = h2 x P, here Phenotype is 4 cm
= 0.6 x 4
= 2.4 cm
iv) The average wing length of the progeny of the selected cockroaches is addition of the mean wing length of the population and expected response (R)
R = Narrow sense heritability (h2) X Selective differential (S)
R = h2 x S
= 0.6 x 1.5
= 0.9
therefore, average wing length = 2.5 + 0.9
= 3.4 cm