Dihybrid Cross And Linkage

Genetic linkage occurs when two genes are located close together on the same chromosome and therefore tend to be inherited together rather than assorting independently. In a testcross, if the two genes were unlinked, all four phenotypic classes would appear in roughly equal 1:1:1:1 proportions because of independent assortment during meiosis. When parental (non-recombinant) types far exceed recombinant types, it means crossing over between the two loci is infrequent, indicating the genes are physically linked. The option claiming independent assortment is wrong because that would yield equal frequencies of all combinations, contradicting the observed excess of parental types. A lethal gene would distort survival ratios but would not specifically produce an excess of parental combinations. Incomplete dominance affects the phenotype of heterozygotes, not the relative frequency of recombinant gametes, so it is irrelevant here. As Morgan demonstrated in Drosophila and as recorded in NCERT Class 12, Chapter 5 (Principles of Inheritance and Variation), tightly linked genes show low recombination frequency. As a logical check, fewer recombinants imply less crossing over, which is exactly what physical proximity of linked genes predicts, confirming linkage.