Final answer:
The F2 generation resulting from the intercross of F1 individuals with closely linked genes Ad and Da will exhibit only the parental phenotypes Ad and Da, in a 1:1 ratio due to no recombination between the genes.
Step-by-step explanation:
When two genes are so closely linked on a chromosome that no recombination is observed between them, the F1 offspring will only produce gametes identical to those of the parental generation. In the scenario described, one parent is homozygous for Ad (AdAd) and the other is homozygous for Da (aDaD). As a result, the F1 generation will only have Ad or Da gametes. When these F1 individuals are intercrossed, the F2 generation will exhibit only the parental phenotypes, Ad or Da, because there are no recombinant genotypes due to the lack of crossing over.
The F2 phenotypes observed will be Ad and Da, with an expected ratio of 1:1 because each F1 individual can only pass on the alleles they received from their parents, with one allele of A being linked to d and one allele of D being linked to a. No new allele combinations are produced. This stands in contrast to unlinked genes which, due to independent assortment, would produce a 9:3:3:1 ratio in a dyhybrid cross.