Question

Lesch Nyhan disease is an X-linked recessive disorder that causes neurological damage in human beings. A survey of 500 mates from a Caucasian population revealed that 20 were affected with this disorder.

What is the frequency of the normal allele in this population?

• A. 9.6
• B. 0.8
• C. 0.096
• D. 96

Answer 1

The correct option is B 0.8

It is given that out of 500 mates from a Caucasian population, 20 were affected by X-linked recessive disorder Lesch Nyhan disease. It means frequency of the recessive allele in 20/500 = 0.04 and of the dominant allele is 100 - 0.04 = 0.96.

Suppose, p is dominant allele and q is recessive allele.

We know that p${}^2$ + 2pq + q${}^2$ = 1.

Here, p${}^2$ = AA, 2pq = 2Aa and q${}^2$ = aa.

It is given that q${}^2$ = 0.04. Hence, q = 0.2.

Now, p + q = 1.

So, p = 1 - 0.2 = 0.8.

Hence, the frequence of the normal allele is 0.8.

Thus, the correct answer is '0.8.'