Tay-Sachs disease occurs almost exclusively among Ashkenazi Jews, with an incidence of 1/3600. The frequency of carriers of the Tay-Sachs gene is which of the following ?
A 1/4
B 1/30
C 1/60
D 1/600
B..
The frequency can be calculated from the Hardy-Weinberg law, in which the carrier frequency is equal 2 pq. q is calculated by taking the square root of the incidence, which gives the frequency of the gene, 1 in 60, and p equal to 1-q, or 60/60-1/60, which gives 59/60. As can be seen here, in most cases of rare diseases, p becomes equal to 1, and the carrier frequency becomes 2q, or 2 times 1/60, which gives the frequency of 1/30.