In cows, hornlessness dominates the horn gene. What is the genotype: a) in horned ones?

In cows, hornlessness dominates the horn gene. What is the genotype: a) in horned ones? A) What is the probability of a hornless calf appearing in F1 if x is a hornless heterozygous female and a hornless male organism?

Let’s designate the dominant gene that causes hornlessness in cows by the letter “A”, then the recessive gene that causes horns will be “a”.

Horned cows are homozygous for the recessive trait and carry the aa genotype.

A hornless heterozygous cow will have the genotype Aa, hornless (hornless) bull A_ (the second gene is not known, since one dominant gene in the allele is sufficient for the absence of horns).

A hornless calf will have the A_ genotype (one dominant allele is sufficient, so the second gene is unknown).

Let’s consider both options.

Option 1.

The bull is homozygous for the dominant trait – AA, it produces A.

Cow – gametes A and a. The offspring of such a pair will have genotypes AA and Aa, and they will all be hornless.

Option 2.

The bull is heterozygous – Aa, produces gametes A and a, like a cow.

In this case, the offspring will have genotypes: AA, Aa and aa. Phenotypic splitting will occur: 25% of the likely offspring will have horns.

Answer: a) Horned cows have a homozygous recessive genotype aa.

b) If a bull is homozygous for the dominant sign of hornlessness, then the probability of a hornless (hornless) calf in this pair of individuals is 100%; if the bull is heterozygous – 75%.