Gujarati
Hindi
6.Evolution
medium

A population is in Hardy- weinberg equilibrium for a gene with only two alleles. If the gene frequency of an allele $A$ is $0.7$, the genotype frequency of $Aa$ is

A

$0.21$

B

$0.42$

C

$0.36$

D

$0.7$

(AIIMS-2014) (AIIMS-2016)

Solution

For a gene with two alleles, $A$ (dominant) and $a$ (recessive), if the frequency of $A$ is $p$ and the frequency of $a$ is $q$, then the frequencies of the three possible  genotypes ( $AA,\,Aa,$ and $aa$ ) can be expressed by the Hardy-Weinberg equation :

                            $p^2 + 2pq + q^2 = 1$

where, $p^2 =$ frequency of $AA$ (homozygous dominant) individuals, $2pq =$ frequency of $Aa$ (heterozygous) individuals and $q^2 =$ frequency of $aa$ (homozygous recessive) individuals. The equation can be used to calculate allele frequencies if the numbers of homozygous recessive individuals in the population is known.

Here, $p = 0.7$ and $q = 0.3$ (given)

$\therefore  $   $2pq$ (frequency of heterozygote)

$= 2 \times 0.7 \times 0.3 = 0.42$

Standard 12
Biology

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