Question

In cattle, the cam color red and white are two dominant traits that express equally in F1 to produce roan (red and white color in equal proportion). If F1 progeny are self-bred, the resulting progeny in F2 will have a phenotypic ratio (red: roan: white) is
A. $1:1:1$
B. $3:9:3$
C. $1:2:1$
D. $3:9:4$

Answer 1

When alleles of the same gene are present in a living organism and both genes are expressed. Instead of one trait being dominant over the other, both traits appear as known as codominance. In this question, it is given that the two dominant traits are equally expressed in the F1 generation, so this is a clear case of codominance.

Complete answer: Here it is given that cam color red and white are two dominant traits. Let RR represents the gene that code for cam color red and WW represents the gene that code for white color and when an organism containing these two genes are crossed :

Genes which are crossed	R	R
W	RW	RW
W	RW	RW

Here both genes are expressed dominantly, hence here it is codominance and the cattle produced in the F1 generation are in roan color.
When the F1 progenies selfing are carried out:

RW	R	W
R	RR	RW
W	RW	WW

1 RR: 2 RW:1 WW
1 Red: 2 Roan: 1 White cattle are produced in F2 progeny.
Therefore option C is correct.

Note: The observable physical properties of an organism are known as phenotype whereas an organism’s complete set of heritable genes or genes that can be passed down from parents to offspring is known as genotype.