Final answer:
The observed outcome of only black guinea pig offspring can be attributed to random chance, the small sample size, or the impact of linkage between the fur color gene and a lethal recessive allele, which might be reducing the viability of offspring with the recessive fur color genotype.
Step-by-step explanation:
In the scenario described with the guinea pigs, the expectation from a cross between two heterozygous individuals (Bb) for a dominantly inherited black fur trait would typically result in a phenotypic ratio of 3:1, with approximately 75% displaying the dominant black fur and 25% displaying the recessive white fur. However, the presence of only black offspring among the first 12 progeny indicates a deviation from the expected ratio. This outcome can be due to random chance in a small sample size, or it can be potentially influenced by linkage between the fur color gene and a lethal recessive allele that is 1 cM away, which may reduce the viability of offspring with the bb genotype, hence not surviving to be observed. The lethal allele is to remove the homozygous recessive (bb) individuals from the progeny, leaving a greater proportion of black-colored offspring. Considering the cM distance, full linkage is unlikely, but because the linkage is so tight, there is a reduced probability of recombination, which could contribute to fewer white offspring.
It is also important to note that concepts such as epistasis, as seen in other organisms like mice, where a separate gene can influence the expression of another gene (e.g., coat color), could also provide insight into other genetic phenomena that might occur if similar interactions exist in guinea pigs, which is not indicated here but can be an additional factor in other contexts.