Q.53 In a randomly mating population, the frequency of ‘A’ allele is 0.7. What is the
frequency of ‘Aa’ genotype in the next generation according to Hardy–
Weinberg’s law? (up to two decimal places)
The frequency of the Aa genotype in the next generation is 0.42. Hardy-Weinberg equilibrium predicts this value precisely for a randomly mating population with no evolutionary forces acting.
Step-by-Step Calculation
Given the frequency of allele A (p) = 0.7, the frequency of allele a (q) equals 1 – p = 0.3. The heterozygous genotype Aa frequency is calculated using the formula 2pq, where substitution yields 2×0.7×0.3=0.42. This result holds for the next generation under random mating, as equilibrium genotype frequencies stabilize immediately after one generation of panmixia.
Hardy-Weinberg Assumptions
Random mating ensures allele combinations form predictably without preference. The population must be infinitely large to prevent genetic drift, with no mutation, migration, or selection altering frequencies. Violations like non-random mating or small population size would deviate from the expected 0.42 Aa frequency.
Option Analysis
Common multiple-choice options for this problem include 0.09, 0.21, 0.42, and 0.49.
- 0.09 represents q² (aa homozygote frequency: 0.3²=0.09), not heterozygotes.
- 0.21 equals pq without the factor of 2, ignoring both Aa configurations (A from male, a from female; vice versa).
- 0.42 is correct as 2pq, accounting for all heterozygous combinations.
- 0.49 represents p² (AA homozygote: 0.7²=0.49).
CSIR NET Applications
For CSIR NET Life Sciences preparation, recognize that genotype frequencies sum to 1: p²+2pq+q²=0.49+0.42+0.09=1. This problem tests understanding of equilibrium in randomly mating populations, crucial for evolutionary biology and genetics sections. In a population of 200, expected Aa individuals would be 0.42×200=84, matching similar exam scenarios.
Genotype Frequency Table
| Genotype | Frequency | Calculation |
|---|---|---|
| AA | 0.49 | p² = 0.7² |
| Aa | 0.42 | 2pq = 2×0.7×0.3 |
| aa | 0.09 | q² = 0.3² |
Real-World Relevance
Medical genetics uses these calculations to estimate carrier frequencies for recessive disorders. Conservation biology applies them to monitor allele frequencies in endangered species under random mating assumptions. Deviations signal evolutionary forces, aiding research in population dynamics.
