6. A cross between hens with different comb shape was carried as shown in figure.

The conclusion which can be drawn is
(1) Single gene is involved for comb shape
(2) Two independent segregating genes are involved
(3) Two genes are showing collaboration for phenotype
(4) Four independent segregating alleles are involved

Explanation of the cross

• Phenotypes and underlying genotypes for comb shape in chickens are classically:

  • Walnut comb: R_P_ (both dominant alleles present).

  • Rose comb: R_pp.

  • Pea comb: rrP_.

  • Single comb: rrpp.

• Crossing rose (Rpp) × pea (rrPp) gives F1 walnut (RrPp).

• Selfing F1 (walnut × walnut) yields F2:

  • 9 R_P_ → walnut

  • 3 R_pp → rose

  • 3 rrP_ → pea

  • 1 rrpp → single

• This 9:3:3:1 distribution matches the figure (9 walnut, 3 rose, 3 pea, 1 single), proving that two independent genes interact to determine comb shape.

Option-wise explanation

1. Single gene is involved for comb shape

• A single gene with multiple alleles would not give a 9:3:3:1 dihybrid ratio.

• The F2 pattern clearly shows involvement of two loci.

2. Two independent segregating genes are involved

• Only partially correct; it notes two genes, but ignores their interaction.

• A simple dihybrid with no interaction gives 9:3:3:1 across two traits, not four distinct phenotypes of one trait.

3. Two genes are showing collaboration for phenotype – correct

• “Collaboration” means epistatic interaction: both genes together determine a single trait (comb shape).

• Dominant alleles at both loci collaborate to produce walnut; individual dominants give rose or pea; double recessive gives single.

4. Four independent segregating alleles are involved

• Misleading: while four phenotypes exist, they arise from combinations of two loci (R/r and P/p), not four separate independently segregating alleles at different loci.

Thus, the conclusion from the 9:3:3:1 comb-shape cross is that two genes interact (collaborate) to produce the observed comb phenotypes.