Question

Lesch Nyhan disease is an X-linked recessive disorder that causes neurological damage in human beings. A survey of $500$ mates from a caucasion population revealed that $20$ were effected 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 $0.8$

Answer is B.

Total individuals- 500

Affected individuals- 20

Lesch Nyhan syndrome is a X-linked recessive disorder which means that the gene mutation is carried out by the mother and passed on to her son. Female are the carriers in this disorder.

Now, 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)