GATE 2021 BT – Question 58
A randomly mating population has Y allele frequency 0.70 in sperm and eggs. The Y/y heterozygote frequency (two decimal places) is _______.
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Correct answer: 0.41 to 0.43
Explanation
Under random mating, the **Hardy-Weinberg** law gives the genotype frequencies in the next generation.
Let $p=0.70$ be the frequency of $Y$ and $q=1-p=0.30$ the frequency of $y$ (the same in sperm and eggs).
The heterozygote $Yy$ can be formed in two ways ($Y$ from sperm and $y$ from egg, or $y$ from sperm and $Y$ from egg):
$$f(Yy)=2pq=2\times0.70\times0.30=\mathbf{0.42}.$$