6
Suppose that the recessive individuals (‘aa’, like lethal or sterile genes) of a large random mating population are intended to
be entirely eliminated from the population and that only the dominants are allowed to mate and reproduce. The zygotic
proportions of the various genotypes (AA, Aa, aa) in the population before such a selection (against recessives) are given as
(p2, 2pq, a2) respectively. The frequency of ‘A’ after such a selection in the next generation is
EXPLANATION
Population Genetics
- Complete Selection Against Recessive Lethal Alleles:
- Initial genotype frequencies under Hardy-Weinberg equilibrium: $AA (p^2), Aa (2pq), aa (q^2)$.
- When all homozygous recessive individuals ($aa$) are completely eliminated ($s = 1$), the surviving breeding population consists only of $AA$ and $Aa$:
- Frequency of Allele A in Next Generation ($p_1$):
- The surviving gametes producing allele $A$ come from $AA$ (weight $p^2$) and $Aa$ (weight $\frac{1}{2}(2pq) = pq$):
- Change in Recessive Frequency ($\Delta q$):
- $q_1 = \frac{q}{1 + q} \implies \Delta q = q_1 - q = -\frac{q^2}{1 + q}$.
- In the options, Option 3 corresponds to the formula with denominator $(1 + q)$.
- Conclusion: Matches Option 3.
Correct option: (3) -7/ (1+ 4)
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