CBSE Class 10 Answered

Gene flow is the movement of gene variants from one population to another. For example, African humans usually have a gene variant called DuffyO which protects against a form of malaria. European humans usually do not have this variant. However, intermarriage between African and European people is gradually introducing DuffyO into the European gene pool. Thus, slowly the variant would be introduced in the entire population and they would be consequently having the same genetic composition and no new species would be formed.

Genetic drift is a random change in the frequency of gene variants within a population. For example, if an individual who carries a rare gene variant happens to have more children than usual, then there will be more copies of the rare gene in the next generation. This can eventually cause a population of organisms to be genetically distinct from its original population and result in the formation of a new species, thus favouring speciation.