Explanation:

Mendel's experiments on pea plants led him to formulate the laws of inheritance, which are now known as Mendelian genetics. One of the important concepts in Mendelian genetics is the principle of independent assortment. This principle states that different genes on different chromosomes segregate independently during meiosis, which means that the inheritance of one gene does not affect the inheritance of another gene.

Dihybrid Cross:

A dihybrid cross is a genetic cross between two individuals that differ in two traits. For example, if we cross a pea plant that is homozygous dominant for yellow seed color and round seed shape (YYRR) with a pea plant that is homozygous recessive for green seed color and wrinkled seed shape (yyrr), we can observe the inheritance of two traits simultaneously.

Parental Combinations in F2:

In the F2 generation of a dihybrid cross, we expect to see four phenotypic ratios: 9:3:3:1. This means that 9/16 of the offspring should have both dominant traits, 3/16 should have one dominant and one recessive trait, 3/16 should have the other dominant and recessive trait, and 1/16 should have both recessive traits.

If there were only parental combinations in F2 of a dihybrid cross, it would mean that all the offspring have the same combination of traits as one of the parents. For example, if the YYRR parent was the only one to produce offspring with yellow and round traits, then all the offspring in the F2 generation would also have yellow and round traits.

Linkage:

The only way that we could observe only parental combinations in the F2 generation is if the two genes were linked on the same chromosome. Linkage occurs when two or more genes are located close together on the same chromosome, which means that they are likely to be inherited together rather than independently.

Repulsion:

Repulsion is the opposite of linkage. When two genes are in repulsion, they are on the same chromosome but with opposite alleles. In this case, the dominant allele of one gene is linked with the recessive allele of the other gene.

Conclusion:

Therefore, if we observed only parental combinations in the F2 generation of a dihybrid cross, it would suggest that the two genes were linked on the same chromosome, and Mendel might have discovered linkage instead of independent assortment.