In horses, black hair color is dominant to chestnut hair color. If the black horse is homozygous, what is its genotype? If the black horse is heterozygous, what is its genotype?
The correct answer and explanation is:
Correct Answer:
- Homozygous black horse genotype: BB
- Heterozygous black horse genotype: Bb
Explanation (300 words):
In genetics, traits like coat color in horses are determined by alleles—different forms of a gene. For this example, black coat color is dominant over chestnut coat color, which is recessive.
Let’s assign symbols to represent the alleles:
- B = allele for black coat (dominant)
- b = allele for chestnut coat (recessive)
Since black is dominant, a horse only needs one B allele to appear black. Chestnut, on the other hand, only appears when the horse has two recessive alleles (bb).
Homozygous Black (BB):
A homozygous horse has two identical alleles. So, if a black horse is homozygous for the black trait, it must have two dominant black alleles:
- Genotype = BB
- This horse will always pass on the black allele to its offspring.
- When bred with another horse, it ensures the black trait is strongly expressed, especially if the mate also carries at least one B allele.
Heterozygous Black (Bb):
A heterozygous horse has two different alleles: one dominant and one recessive.
- Genotype = Bb
- Even though it has one chestnut allele (b), the dominant black allele (B) masks its effect, so the horse appears black.
- However, it can pass on the chestnut allele (b) to offspring. If mated with another Bb or bb horse, some offspring could be chestnut.
Understanding these genotypes is critical in horse breeding, as it allows breeders to predict the coat colors of potential offspring. A Punnett square can help visualize the possible combinations and outcomes.
In summary, BB is the genotype of a homozygous black horse, and Bb is the genotype of a heterozygous black horse.