Final answer:
The genotype of a heterozygous short-haired guinea pig is Ss, where 'S' is the dominant allele for short hair and 's' is the recessive allele, possibly for long hair.
Step-by-step explanation:
The genotype of a heterozygous short-haired guinea pig would be Ss. This indicates that the guinea pig has one allele for the dominant trait, short hair (S), and one allele for the recessive trait, which may be long hair (s). Therefore, the correct answer is B) Ss. In genetics, being heterozygous means having two different alleles for a particular gene, one inherited from each parent. The dominance of the short hair trait over the possible long hair trait results in a phenotype of short hair, even though the guinea pig carries both alleles.