Question

In a genetic cross between plants bearing violet flowers and green seeds (VVGG), and white flowers and yellow seeds (vvgg), the following phenotypic distribution was obtained in the F$_2$ progeny (assume both parents to be pure breeding for both traits, and self-cross at F$_1$ generation):
i) 2340 plants with violet flowers and green seeds
ii) 47 plants with violet flowers and yellow seeds
iii) 43 plants with white flowers and green seeds
iv) 770 plants with white flowers and yellow seeds
Which one of the following interpretations explains the above phenotypic distribution?

• A. Same genes control both flower and seed colors
• B. Genes for flower and seed colors are genetically interacting
• C. Genes for flower and seed colors are present on the same chromosome
• D. Flower color in this plant species is a polygenic trait

Hint:

Linked genes do not follow independent assortment. Recombinants appear in small numbers due to limited crossing over — a key sign of linkage.

Answer 1

The Correct Option is C

Step 1: Analyze the phenotypic ratio.
The observed distribution shows:
Violet-green (2340), Violet-yellow (47), White-green (43), White-yellow (770).
Step 2: Compare with expected Mendelian ratio.
If genes were independently assorting, a dihybrid cross (VVGG × vvgg) would produce F$_2$ phenotypes in a 9:3:3:1 ratio.
However, the numbers here are highly skewed — most offspring show parental combinations (violet-green and white-yellow), while recombinants (violet-yellow and white-green) are rare.
Step 3: Interpret the deviation.
Low frequency of recombinant phenotypes (47 and 43) suggests that the genes for flower color and seed color are linked — i.e., located close together on the same chromosome.
Crossing over between them is infrequent, leading to a majority of parental-type combinations.
Step 4: Conclusion.
Thus, the distribution arises due to genetic linkage, meaning both genes are on the same chromosome.