Consider a hypothetical quantitative weight trait affected by five loci. Assume

Question

Consider a hypothetical quantitative weight trait affected by five loci. Assume complete dominance at all loci, and no epistasis. The independent effect of each dominant allele is +8 lb and the independent effect of each recessive allele is -2 lb. The population mean for the trait is 500 lb.

a. If an animal is heterozygous at all loci, and the environmental effect is -12 lb, what are the values for the animal’s breeding value, genotypic value, gene combination value, and phenotypic value?

b. If an animal is homozygous dominant at three loci and homozygous recessive at the other two, and the environmental effect is +10, what are the values for the animal’s breeding value, genotypic value, gene combination value, and phenotypic value?

c. Which animal would produce the heaviest offspring, on average? Why?

Explanation / Answer

a. the heterozzygouson all loci means: AaBbCcDdEe

so, Breeding Value(bv): {+8+(-2)]*5= 30

genotypic value (G)= BV * frequency of the species= 30*0.50=15

frequency is calculted as in complete dominance frequency of heterozygous is same as that of homozygous

gene combination value(GCV)= G-BV= 15-30=-15

phenotypic value= U(population mean)+G+E(enviromental value)=500+(-12)=15=503

b. for AABBCCddee :

BV=16+16+16-4-4=40

G=40*0.5=20

p= 530

GCV=-20

c.the heavy offsprings will be produced by the animal with homozygousity dominance at 3 loci and homozygousity recessiveness at 2 loci because of more genotypic value if compared to the animal with heterozygous at all five loci.

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