Lack of independent assortment of two genes A and B in the fruit fly Drosophila due to :
Mendel’s law of independent assortment states that when the parent differs from each other in two or more pairs of contrasting characters, the inheritance of one pair of the factor is independent of the other. For the character to assort independently they should be located on separate nonhomologous chromosomes. Genes present on the same chromosome show linkage. It means that these characters remain together and thus low numbers of combinations are formed. This phenomenon is called linkage such genes are called linked genes. So A and B are linked genes.