Question

Write an explanatory note on: Hardy-Weinberg principle.

Hint:

Hardy-Weinberg describes a population with no evolutionary change; the equation is p squared + 2pq + q squared = 1.

Answer 1

Step 1: Understanding the Concept:
The Hardy-Weinberg principle describes what happens to the genetic makeup of a population when no evolutionary forces are acting on it, a useful reference point for detecting when evolution is actually happening.

Step 2: State the principle.
It states that the allele frequencies and genotype frequencies in a population remain constant, generation after generation, as long as the population is in a state of genetic equilibrium, meaning no mutation, no migration, random mating, an infinitely large population size, and no natural selection are occurring.

Step 3: Give the mathematical form.
For a gene with two alleles of frequency $p$ and $q$ (where $p+q=1$), the genotype frequencies in the population are described by the equation $p^2+2pq+q^2=1$, where $p^2$ is the frequency of the homozygous dominant genotype, $2pq$ is the frequency of the heterozygous genotype, and $q^2$ is the frequency of the homozygous recessive genotype.

Step 4: State its practical use.
If the actual genotype frequencies observed in a real population differ from those predicted by this equation, it signals that one of the assumed conditions is being violated, and evolutionary change is likely taking place.

Final Answer:
The Hardy-Weinberg principle says allele and genotype frequencies stay constant across generations without evolutionary influences, summarised by \( p^2+2pq+q^2=1 \); a deviation from this is used to detect evolution in a population.