In a population, the frequency of an allele measured in a new generation differs from the value expected by the Hardy-Weinberg principle. What does this difference (and its direction) indicate?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → The extent of evolutionary change
The Hardy-Weinberg principle gives the expected allele frequencies of a population that is not evolving. When the frequency actually measured differs from the expected value, the population has moved away from genetic equilibrium. The size and direction of this difference tell us how much evolutionary change has taken place.
Option (1) The population is in genetic equilibrium — Incorrect. A population in genetic equilibrium shows no difference between measured and expected frequencies, because its allele frequencies stay constant.
Option (2) The extent of evolutionary change — Correct. The difference, and its direction, indicates the extent of evolutionary change.
Option (3) The frequency of heterozygous individuals in the population — Incorrect. The frequency of heterozygous (Aa) individuals is given by the term 2pq of the equation. It is one part of the expected values, not what the difference between measured and expected values shows.
Option (4) The total number of genes and their alleles in the gene pool — Incorrect. The gene pool is the total genes and their alleles in a population. The difference in one allele frequency does not measure the size of the gene pool.
NCERT Extract:
Hardy-Weinberg Principle – “… Hence, p2+2pq+q2=1. This is a binomial expansion of (p+q)2. When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change. Disturbance in genetic equilibrium, or Hardy- Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.”