In a certain population each of three serious neuromuscular

In a certain population, each of three serious neuromuscular disorders—autosomal dominant facioscapulohumeral muscular dystrophy, autosomal recessive Friedreich ataxia, and X-linked Duchenne muscular dystrophy—has a population frequency of approximately 1 in 25,000.

What are the gene frequency and the heterozygote frequency for each of these?

Suppose that each one could be treated, so that selection against it is substantially reduced and affected individuals can have children. What would be the effect on the gene frequencies in each case? Why?

Solution

According to HW equilibrium concept,

q2 = 1/25000 = This is genotype frequency.

q = Gene frequency of recessive gene which causes neuromuscular disorders = (1 ÷ 25000) = 0.0063

p = (1-q) = 1-0.0063 = 0.9937 = Gene frequency of dominant gene

2pq = Heterozygote frequency = (2*0.9937*0.0063) = 0.0125

If affected individuals are having children, then it means that there is a cross between two homozygous recessive parents. This cross will further give all affected children only. So, fitness of homozygous recessive genotype becomes 1.

Gene frequency will also change as a result of this; because now the population frequency of these individuals is also increasing.

Please note: For calculating the exact gene frequency, you need to know the new population frequency of homozygous recessive.