In cattle, hornlessness (absence of horns) completely dominates over the presence of horns

In cattle, hornlessness (absence of horns) completely dominates over the presence of horns, and the inheritance of wool color is intermediate … in nature: brown color dominates over white, an intermediate feature is a roan suit. The genes that control the appearance of these traits are located in different pairs of autosomes. A horned roan cow was crossed with a hornless roan bull, one of whose parents was horned. Determine the probability of occurrence among the offspring: a) a white calf; b) a horned calf; c) a brown calf; d) roan with horns.

Let’s designate the gene that causes the hornlessness of cows as B, then the gene that in the homozygous state leads to the development of horns will be b.

Let’s designate the gene that determines the development of brown wool in cows as C, then the gene for white color will be c. Individuals of the roan suit, according to the condition of the problem, will be recorded as Сс.

The horned roan will be bbCc, the eggs it produces are bC and bc.

A hornless roan bull, one of the parent individuals of which had horns and could only pass on the gene for the recessive trait (b), will be written as BbCc. The spermatozoa it produces are ВС, bс, Вс and bС.

All possible offspring of this pair of individuals will look like this:

hornless brown calves (BbCC);

horned roan calves (2 bbСс);

hornless roan calves (2 BbCc);

horned cinnamon calves (bbcc);

horned white calves (bbcc);

hornless white calves (Bbcc).

a) White calves: 2 genotypes out of 8 – 25% probability;

b) Horned calves: 4 genotypes out of 8 – 25% probability;

c) Hornless brown calf: genotype 1 out of 8 – 12.5% ​​probability;

d) Roan horned calf: 2 genotypes out of 8 – 25% probability.