Two strains of rats were selected for increased or decreased pigmentation on the
ID: 268997 • Letter: T
Question
Two strains of rats were selected for increased or decreased pigmentation on the head and back. After 10 generations of selection, the highly inbred high pigmentation strain had a mean pigmentation rating of 3.73, and the highly inbred low pigmentation strain had a mean pigmentation rating of –2.01. The strains were crossed, and the standard deviation for pigmentation rating in the F1 and F2 generations were 0.60 and 0.87, respectively.
(a) Estimate the number of genes affecting pigmentation in these strains.
(b) What is the environmental variance for this trait?
Equations that might be helpful
normal distribution: ?-approx. 68% 2?-approx.95% 3?-approx. 99.7% ? ? ?2-0, + ?2+ CoVfGE) partitioning of total phenotypic variance: partitioning of genotypic variance broad-sense heritability: w-sense heritability : h2_?i narro prediction equation: R-Swhere R-M - M S-M*- M regression coefficent: bor- CoV(QP)-- b0MP-Covio,MP) _½?- MP number of genes contributing to quantitative trait: n-Explanation / Answer
Pigmentation is a quantitative trait.
Environmental variance, VE = 3.73 + (-2.01) / 2 = 1.72 /2 = 0.86
VE = (0.60 +0.86) /2 = 1.46 /2 = 0.73
Phenotypic variance, Vp = 0.87
So, Genetic variance, Vg = Vp - VE = 0.87-0.73 = 0.14
Number of genes involved in this quantitative trait (n) = D2 / 8*Vg
where D = difference of mean of two parents
Hence, n = (3.73 +(-2.01))2 / 8*0.14 = 32.94 / 1.12 = 29
b. Environmental variance, VE is approaching 1 means environment have an impact on this trait.
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