Sickle cell disease (SCD) is found in numerous populations whose ancestral homes are in the malaria belt of Africa and Asia. SCD is an autosomal recessive disorder that results from homozygosity for a mutant β-globin gene allele. Data on one affected population indicates that approximately 8 in 100 newborn infants have SCD. What are the frequencies of the wild-type (βᴬ) and mutant (βˢ) alleles in this population?

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance refers to a pattern where two copies of a mutant gene (one from each parent) are necessary for an individual to express a recessive trait, such as sickle cell disease. In this case, individuals with SCD are homozygous for the mutant β-globin gene allele (βˢ), while carriers have one normal allele (βᴬ) and one mutant allele.

Hardy-Weinberg Principle

The Hardy-Weinberg principle provides a mathematical framework for understanding allele frequencies in a population at equilibrium. It states that the frequencies of alleles and genotypes will remain constant from generation to generation in the absence of evolutionary influences, allowing for the calculation of allele frequencies based on observed genotype frequencies.

Allele Frequency Calculation

Allele frequency calculation involves determining the proportion of a specific allele within a population. For sickle cell disease, if 8% of newborns are affected (homozygous recessive), the frequency of the mutant allele (βˢ) can be calculated using the Hardy-Weinberg equation, where q² represents the frequency of the recessive phenotype, allowing for the derivation of both q (frequency of βˢ) and p (frequency of βᴬ).