Question

In horses the allele for black coat (B) is dominant to the allele for chestnut coat (b) and the allele for trotting gait (T) is dominant to the allele for running gait (t).

1) Predict the phenotype ratio for the offspring of heterozygous black heterozygous trotting horse with a chestnut running horse.

2) Predict the phenotype ratio for the offspring of a homozygous black heterozygous trotting horse with a chestnut running horse.

Answer 1

1. Here, we have a heterozygous horse (BbTt) crossed with a horse homozygous recessive for both traits (bbtt). As the only gamete the latter horse can offer is bt, the genotypes of the offsprings will look like:

	BT	Bt	bT	bt
bt	BbTt (black, trotting)	Bbtt (black, running)	bbTt (chestnut, trotting)	bbtt (chestnut, running)

All the horses have will have different phenotypes, so the phenotypic ratio would be 1:1:1:1

2. The cross is between homozygous black heterozygous trotting (BBTt) and chestnut running (bbtt)

	BT	Bt
bt	BbTt (black, trotting)	Bbtt (black, running)

From the above, we can see that the phenotypic ratio is 1:1