Hardy-Weinberg Law — 2017 Paper I

Approach

• Demand of Question:State the Hardy-Weinberg principle, its assumptions, equation and anthropological significance.
• Structuring the Response: Define equilibrium; present p+q and genotype equations; list assumptions; explain uses in population genetics and the meaning of deviation.
• Key Dimensions to Cover:Hardy and Weinberg (1908); allele and genotype frequencies; random mating, large population, no selection/migration/mutation; baseline model.

Model Answer

Introduction The Hardy-Weinberg Law, formulated independently by mathematician G.H. Hardy and physician Wilhelm Weinberg in 1908, is the foundational principle of population genetics. It states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences.

Body

1. The EquationIf a trait is controlled by two alleles, A(dominant) and a (recessive), with frequencies p and q respectively:

• Allele Frequency Equation: $p + q = 1$
• Genotype Frequency Equation: $p^2 + 2pq + q^2 = 1$ (Where $p^2$ = frequency of homozygous dominant (AA); $2pq$ = heterozygous (Aa); $q^2$ = homozygous recessive (aa)).

2. Core AssumptionsFor genetic equilibrium to exist, five evolutionary forces must be absent:

1. Infinite/Very Large Population Size (no genetic drift).
2. Random Mating (panmixia; no assortative mating or inbreeding).
3. No Mutation (alleles do not change).
4. No Gene Flow/Migration (no alleles enter or leave the population).
5. No Natural Selection (all traits have equal survival and reproductive success).

3. Anthropological Significance

• The Null Hypothesis of Evolution: Real human populations rarely meet all these conditions. The law acts as a baseline/null model. When observed genotype frequencies deviate from Hardy-Weinberg expectations, it proves that evolutionary forces (like natural selection or drift) are actively operating on that population.
• Carrier Estimation: It allows physical anthropologists to calculate the frequency of hidden carriers (heterozygotes, $2pq$) for recessive genetic disorders (e.g., Sickle Cell Anemia) in a population, aiding in genetic counseling.

Conclusion The Hardy-Weinberg principle is not a claim that evolution does not occur. Rather, by defining the exact mathematical conditions under which evolution stops, it provides anthropologists with the standard yardstick to measure the rate and direction of human evolutionary change.