In this scenario, we have a homozygous white horse (CWCW) and a homozygous black horse (CBCB). The coat color gene follows a codominant inheritance pattern.
When these two horses are bred together, the offspring will inherit one allele from each parent:
- From the white horse (CWCW), the offspring will receive a C allele (C for white).
- From the black horse (CBCB), the offspring will receive a C allele (C for black).
This results in all offspring being heterozygous (CWCB). In codominance, both alleles are expressed equally, so the offspring will display a roan coat, which is a mix of both colors.
Therefore, 100% of the offspring will be roan.
The likely correct response is: 100%.