The 9:3:3:1 ratio of law of independent assortment can be affected by

Explanation

Independent assortment requires the two genes to be on different chromosomes, so genes linked on the same chromosome travel together and the dihybrid ratio departs from 9:3:3:1, with parental combinations over represented. Genetic drift and small population size shift allele frequencies across generations rather than distorting the ratio within a single cross. Crossing over partly restores the expected ratio by separating linked genes.