Final answer:
The possible genotype from a cross between homozygous black-haired (BB) and homozygous blonde-haired (bb) individual is heterozygous Bb only.
Step-by-step explanation:
The genotype(s) resulting from a cross between an individual homozygous for black hair (BB) and an individual homozygous for blonde hair (bb) is C) Bb only. This scenario is an example of a monohybrid cross, where two homozygous parents differing in a single trait are crossed producing monohybrid offspring.
In the given cross, the individual with the BB genotype can only produce gametes with the B allele, while the individual with the bb genotype can only produce gametes with the b allele. Since both alleles are different, all offspring resulting from this cross will receive one B allele from the black-haired parent and one b allele from the blonde-haired parent, resulting in a Bb genotype for all offspring. This single genotype represents the heterozygous condition for the hair color trait.