Two inbred strains of com were crossed to produce an F_1. which was then intercr

Question

Two inbred strains of com were crossed to produce an F_1. which was then intercrossed to produce an F:. Data on car length from a sample of F_1 and F_2 individuals gave phenotypic variances of 15.2 cm^2 and 27.6 cm^2, respectively. Why was the phenotypic variance greater for the F_2 than for the F_1 The narrow-sense heritability for abdominal bristle number in a population of Drosophila is 0.3. The mean bristle number is 12. A male with 10 bristles is mated to a female with 20 bristles, and a large number of progeny are scored for bristle number. What is the expected number of bristles among these progeny?

Explanation / Answer

Ans 3. The phenotypic variances were greater in case of F2 as compared to F1 because of independent assortment of chromosomes and recombination, likely to have a unique multilocus genotype. Hence the phenotypic variances would arise due to genetic component and environmental component, leading to greater variances. For the F1, Vg = 0 because they are all genetically identical and heterozygous; for the F2, Vg > 0 because genetic differences result from the segregation and independent assortment of genes.

Ans 4. (15 - 12)(0.3) + 12 = 12.9 bristles.Hence the expected number of bristles among the progeny would be 12.9.

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