In a North European population, the birth incidence of cystic fibrosis is approximately 1 in 2500 live births. Assuming Hardy-Weinberg equilibrium, the carrier frequency in this population is approximately:

• A 1 in 2500
• B 1 in 100
• C 1 in 25 ✓
• D 1 in 5

Explanation

For an autosomal recessive disease, incidence q squared equals 1 in 2500, so q equals 1 in 50 (0.02). Carrier frequency is 2pq, which approximates 2q when q is small, giving roughly 1 in 25. Students who forget to take the square root may choose 1 in 1250, and those who mistake incidence for the allele frequency may choose 1 in 2500. Carrier screening panels use this derived figure to counsel couples.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.