Alkaptoneuria is a recessive genetic disorder found among North American populations at a frequency of about 1 in 500,000 births. How frequently would you expect this defect to be expressed among children of second cousin marriages

The correct answer is - 1/41,493

Explanation:

Let assume the frequency of the two possible same allele genotype (dominant and recessive) in an inbred population is p and q. Then the frequency of heterozygotes (H) is denoted as:

2pq + 2pqF.  ( where F is the inbreeding coefficient).

The frequency of the two different hoozygotes in inbred population can be calculated as:

p2 + pqF and q2 + pqF. (Where p and q are the allele frequency of the dominant and recessive phenotype.

Given: Frequency of Alkaptonuria (q 2) = 1:500, 000

=> q = 1/707

p = 706/707 ( Approx values)

solution:

Inbreeding coefficient (F) = 1/64

Therefore,

Frequency of Alkaptonuria in second cousins= q 2 + pqF

= 1/500, 000 + (706/707 x 1/707) x (1/64)

= 1/500, 000 + 1/45, 248

= 1/41,493 (approx)