Lesch Nyhan disease is an X-linked recessive disorder that causes neurological disorder in human beings. A survey of 500 males from a Caucasian population revealed that 20 were affected with this disorder. What is the frequency of normal allele in this population?

According to Hardy-Weinberg principle-

p² + 2pq + q² =1

Where p is the frequency of the dominant alleles

q is the frequency of the recessive alleles

p² is the percentage of homozygous dominant alleles

q² is the percentage of homozygous recessive alleles

2pq is the percentage of heterozygous alleles

Here in this case-

Frequency of the recessive allele = q² = 20/500 = 0.04

Therefore, q= 0.2

Frequency of the dominant (normal) allele= p

As we know, p + q = 1

So, p = 1–0.2 = 0.8 (normal allele)