Question

Appearance of Walnut-Comb in poultry in a cross between pure Pea-Comb and Rose-Comb animals is due to
A. Duplicate genes
B. Complementary genes
C. Additive genes
D. Collaborative supplementary gene.

Answer 1

Hint: It is a phenomenon in which two non-allelic genes which not only are able to produce their own effects independently when present in the dominant state but can also interact to form a new trait.

Complete answer:
Collaborative Supplementary Genes: They are two nonallelic genes which not only are able to produce their own effects independently when present in the dominant state but can also interact to form a new trait.

Comb types in poultry are an example of collaborative supplementary genes, P and R. When none of these genes is present in the dominant state (pprr), a single comb type character is formed. But when P gene alone is dominant, a pea comb is formed (Pprr, PPrr). If the R gene alone is dominant, a rose comb type character is obtained (ppRr, ppRR). A walnut comb type is formed when both P and R occur together in a dominant state to produce supplementary effect.

When pure pea combed and pure rose combed birds are crossed, all the offspring of F, individuals have walnut comb. On inbreeding the walnut combed birds, the F2 generation comes to have all the four types of combs in the ratio of 9 walnut: 3 pea: 3 rose: 1 single.

Hence, the correct answer is option (D)

Note: Additive genes are those genes that code for the same trait and their effects work together on the phenotype. An example of a function of additive genes is on the eye colour. Several genes work together to determine the colour of the eye of an offspring.