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 revealed that 20 were affected with the 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

Hint: We need to check out frequency of the recessive allele and dominant allele in order to calculate frequency of normal allele. The equation is used where the population is supposed to be in Hardy-Weinberg equilibrium. It states that the genetic variation in a population remains constant from generation to generation in the absence of disturbing factors

Complete answer:
The Hardy-Weinberg equilibrium states that the genetic variation in a population remains constant over generations unless any disturbing factor or mutation occurs in a population. Mutation leads to the introduction of a new allele which disrupts the population.
\[\dfrac{20}{500}=0.04\]
And the frequency of the dominant allele is-
\[100-0.04=0.96\]
To find out the frequency of normal allele, suppose that p is the dominant allele and q is recessive allele.
It is known that- \[\] ${p^2} + 2pq + {q^2} = 1$,
Where,
P and q represent the frequencies of homozygous dominant and homozygous recessive alleles respectively.
Here,
${p^2} = AA,2pq = 2Aa,{q^2} = aa$.
It is given that ${q^2} = 0.04;q = 0.2$
Now, $p + q = 1$
So, $p = 1 - 0.2 = 0.8$
Therefore, the frequency of the normal allele will be $- 0.8$.

So the correct answer is option ‘B’ . 0.8

Note: The Caucasian race is an outdated categorization of human beings which was previously regarded as a separate biological taxon whose classification depends on historical race classifications. It included the ancient and modern populations of all or parts of Europe, Asia, North Africa, and the Horn of Africa.