Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in F1 generation for a dihybrid cross?
When two loci are linked and two heterozygous parents are crossed in a dihybrid cross, the phenotypic distribution in F1 generation deviates from the expected 9:3:3:1 ratio of independent assortment.
The parental type combinations appear in much higher frequency while the recombinant types appear in lower frequency. This occurs because linked genes on the same chromosome tend to be inherited together and do not assort independently.
As demonstrated in Morgan's experiments, one cross showed 98.7% parental types and only 1.3% recombinant types, while another showed 62.8% parental types and 37.2% recombinant types. The degree of deviation from the expected ratio depends on the linkage strength between the two loci.
Explanation
The question asks about the effect of linkage on phenotypic distribution in a dihybrid cross. According to the context from Figure 4.11, Morgan's experiments on linkage showed that when genes are linked, they do not follow Mendel's Law of Independent Assortment. Instead of the expected 9:3:3:1 phenotypic ratio, the parental combinations appear more frequently (98.7% or 62.8% in Morgan's experiments) while recombinant types appear less frequently (1.3% or 37.2%). This happens because linked genes are located on the same chromosome and tend to be inherited together.
Solution Steps
Step 1: Identify that linked genes do not follow independent assortment
Step 2: State that phenotypic ratio deviates from 9:3:3:1
Step 3: Explain that parental types are more frequent than recombinant types
Step 4: Reference Morgan's experimental data showing high parental type percentages (98.7% and 62.8%)