Practice question

For autosomal recessive disorders, affected individuals correspond to q squared, while heterozygous carriers remain phenotypically normal yet transmit mutant allele to offspring. Under Hardy-Weinberg, carrier proportion equals probability of receiving different alleles from two parents, p times q plus q times p, which equals two pq. When q is small, p approximates one, so carrier frequency approximates two q, explaining why carriers greatly outnumber affected homozygotes. Estimating two pq is essential in genetic counseling for cystic fibrosis, Tay-Sachs, and other recessive conditions worldwide population.