Question

A gene locus has two alleles A, a. If the frequency of dominant allele A is 0.4, then what will be the frequency of homozygous dominant, heterozygous and homozygous recessive individuals in the population?
A. 0.36(AA); 0.48(Aa); 0.16(aa)
B. 0.16(AA); 0.24(Aa); 0.36(aa)
C. 0.16(AA); 0.48(Aa); 0.36(aa)
D. 0.16(AA); 0.36(Aa); 0.48(aa)

Answer 1

Hint: Allele frequency refers to how common an allele is in a population. The frequency of the dominant (normal) allele in the population (p) is simply 1 - 0.02 = 0.98 (or 98%).

Complete Answer:
An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Humans are called diploid organisms because they have two alleles at each genetic locus, with one allele inherited from each parent.

Now, let us find the solution from the option.
$\Rightarrow$ Frequency of dominant allele (say p)=0.4
$\Rightarrow$ Frequency of recessive allele (say q) =1−0.4=0.6
$\Rightarrow$ ∴ Frequency of homozygous dominant individuals (AA) = p2 = (0.4)2=0.16
$\Rightarrow$ Frequency of heterozygous individuals (Aa) = 2pq = 2(0.4)(0.6) = 0.48
$\Rightarrow$ Frequency of homozygous recessive individuals(aa) = q2 = (0.6)2 =0.36.

Thus, the correct option is B. i.e. 0.16(AA); 0.24(Aa); 0.36(aa).

Note: A gene is a series of nucleotides (monomers of DNA) that codes for a specific protein. A combination of 3 specific nucleotide base-pairs codes for an amino acid, and combinations of many codes for a protein, which is a long string of amino acids.
- All of the base-pairs involved in making one protein are called the gene.
- An allele is a variant of a gene.
- Each cell has two alleles (one per parent) for each gene: one dominant, one recessive. The dominant allele is the one which actually codes for the protein, while the recessive one does effectively nothing.