Question

A roan bull is bred to three cows. Cow A has the same genotype as roan bull. Cow B is red and Cow C is white. What proportions of roan cows are expected in offsprings of each group of cow?
A. 2,1,1
B. 1,2,1
C. 1,1,2
D. 3,1

Answer 1

Hint: Codominance happens when two copies, or "allele," of the same gene are found in a living thing, and both are expressed. Instead of the fact that one trait is superior over the other, both traits appear.

Complete Answer:
- When red cattle breed with red cattle, the resultant offspring which show both red and white fur, resulting in a mixed coat pattern called "roan." By codominance, a cross between species with two different phenotypes produces offspring with a third phenotype in which both parent traits appear together.
- The colour of the coat in the cows is regulated by two alleles; W (red) and w (white). These two alleles exhibit codominance, and the hybrid genotype (Ww) has a roan coloured coat.

- The genotype of the roan cattle is "Ww," the red one is "WW" and the white one is "ww." A hybrid between a roan bull and a roan cow produces red, roan and white phenotypes at 1:2:1 ratios, respectively.
- The cross between roan bull (Ww) and red cow (WW) develops roan and red phenotypes at a 1:1 ratio.
- The cross between roan bull (ww) and white cow (ww) develops roan and white phenotypes at 1:1 ratio.

The white cow genotype is WW, the red colour genotype is RR, the roan colour genotype is WR. The roan bull has the genotype WR, while the three cows have the genotype WR, RR, WW.

	W	R
W	WW	WR
R	WR	RR

	R	R
W	WR	WR
R	RR	RR

50% OFFSPRING WILL BE ROAN.

	W	W
W	WW	WW
R	WR	WR

50% OFFSPRING WILL BE ROAN.

The proportion of roan cows in the offspring of each cow group is 2,1,1.

The correct answer is option (A) 2,1,1.

Note: Codominance is easy to detect in plants and animals with more than one pigment colour. Spotted cows and flowers with petals in two different colours are examples in codominance.