Question

In short horned cattle, genes for red $(R)$ and white $(r)$ coat colour occur. Cross between red $(RR)$ and white $(rr)$ produced $(Rr)$ roan. This is an example of

• A. incomplete dominance
• B. codominance
• C. complementary genes
• D. epistasis

Answer 1

Answer: (B)

Codominance is the phenomenon, in which both the genes are expressed in $F_1$ generation.

Incomplete dominance phenomenon was discovered by Correns (1903). The hybrid is a fine mixture of the expression of $2$ allele in their homozygous state.
If two genes present on different loci produce the same effect when present alone but interact to form a new trait when present together are called complementary genes, eg, flower colour in sweat pea. The characteristic ratio is $9:7$.
Epistasis is the phenomenon of suppression of phenotypic expression of a gene by a non-allelic gene, which shows its own effect. The gene which males the effect of another is called epistatic gene while the one which is suppressed is called hypostatic gene.