The allele for the black coat colour (B) is dominant over the allele for white coat colour (b) in horses. A cross between two black horses produces a foal with white coat colour. The probability of the second foal having black coat would be

The correct option is B 3/4
The allele for the black coat colour (B) is dominant over the allele for white coat colour (b) in horses. A cross between two black horses produces a foal with white coat colour. The white coat colour foal will be having the genotype bb. This shows that the two parents are heterozygous and have the genotypes Bb and Bb.

When the cross between Bb and Bb is performed, the offsprings produced will be:

BB- black,

Bb- black,

Bb- black

bb- white

There are 3 in 4 chances that the offspring will have black coat colour.

Thus, the correct answer is option '3/4'.