Biology · Evolution · NEET
They are closely linked but not identical. Gene migration is the movement of a section of a population to another place and population. NCERT states clearly: if this gene migration happens multiple times, it is called gene flow. So gene migration is a single or one-time movement of alleles, and gene flow is the repeated migration that keeps mixing alleles between populations. For NEET, both are listed together as one factor that affects Hardy-Weinberg equilibrium.
When a section of a population moves to a new place and joins another population, new genes or alleles are added to the new population. At the same time, those alleles are lost from the old population. Because alleles are gained on one side and lost on the other, the gene frequencies change in both the original and the new population. This is exactly why migration is counted as an agent of evolution.
Hardy-Weinberg equilibrium says allele frequencies stay constant only if there is no migration, no genetic drift, no mutation, no genetic recombination, and no natural selection. Gene flow (gene migration) directly adds and removes alleles, so it changes allele frequencies. Once frequencies change, the population is no longer in equilibrium, and NCERT interprets this change of allele frequency as evolution.
Both change allele frequencies, but the cause is different. Gene flow is change due to actual physical migration of individuals between populations. Genetic drift is change that happens by chance, especially in a small population, with no migration needed. NCERT says: if the same change in allele frequency occurs by chance, it is called genetic drift. So the key word for gene flow is migration, and for genetic drift it is chance.
Gene flow tends to make two populations more similar because it mixes their alleles. Within a single receiving population, it can increase variation by bringing in new alleles. But between populations, it reduces the difference. This is opposite to genetic drift, which usually makes small populations more different from each other. NEET may test this contrast, so remember: gene flow mixes, drift separates.
Which of the following factors will not affect the Hardy-Weinberg equilibrium?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Gene flow is the transfer of alleles from one population to another because individuals migrate and breed there. When migration repeats many times, alleles keep moving between the two populations, changing their allele frequencies.
Yes. The five factors are gene migration or gene flow, genetic drift, mutation, genetic recombination, and natural selection. Gene flow is listed first in NCERT.
The alleles carried by the migrating individuals are lost from the old population, so the old population's allele frequencies also change, not just the new one.
Yes. Because gene flow changes allele frequencies, and any change in allele frequency in a population is interpreted as evolution in the Hardy-Weinberg framework.
It is a high-yield point in the Evolution chapter and is regularly tested as one of the five factors that disturb Hardy-Weinberg equilibrium, often alongside genetic drift.
