In guinea pigs, the allele for a rough coat (R) is dominant over the allele for a smooth coat (r). A heterozygous guinea pig (Rr) and homozygous recessive guinea pig (rr) have a total of nine offspring. Explain how all nine offspring can have smooth coats.

When a heterozygous guinea pig (Rr) is crossed with a homozygous guinea pig (aa), the possible genotype of the offspring contains Rr and rr. Each genotype has a 50% chance of occurring in a specific generation. Nine offspring can have smooth coats as heterozygous (Rr) and homozygous (rr) parents indicate low chromosome recombination frequency (in this crossover). Genes close together on the chromosome indicate low recombination; thus, the crossover would rarely happen.