Question

A strain of heavy mice was crossed with a lighter strain; the F1s were all of intermediate weight. When these F1 mice were interbred, a continuous distribution of adult weights was obtained in the F2 generation. Only about one F2 mouse in 1000 was as heavy as the heavy parent stock. Assuming that the observed inheritance pattern is quantitative, how many genes contribute to this phenotype?

Answer 1

• When more than one genes control the same trait to give additive effect of all the alleles the trait is said to be quantitative or polygenic.
• Quantitative traits are governed by many genes at different loci and each contribute to same amount of phenotype, I.e. the effect of genes is cumulative.
• For calculating number of gene pairs which are responsible for a particular quantitative faith can be determined by calculating the ratio of F2 progeny which resembles one of the extreme phenotype of parent.
• Ratio of F2 progeny which expresses either of the extreme phenotype = 1/4n.
• 5 genes contribute to the weight of mouse.
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