Final answer:
Gray offspring resulting from the breeding of a black swan and a white swan is an example of incomplete dominance, where the phenotype is a blend of both parents' traits.
Step-by-step explanation:
When a black swan and a white swan breed to produce offspring that are gray in color, the most likely explanation for this phenomenon is incomplete dominance. This is a form of inheritance where the phenotype of the heterozygote (gray offspring) is an intermediate phenotype between the two homozygous phenotypes (black and white swans).
To further illustrate this point, if we consider a case where chickens are bred and the first generation results in black chickens with white speckles, when these speckled chickens are interbred, their offspring may show a variety of patterns. According to Mendelian genetics, this could follow a codominance pattern, where both alleles are expressed equally in the phenotype, or continue the pattern of incomplete dominance. Each chicken could have the potential to be speckled, black, or white, depending on the combination of alleles inherited from the speckled parents.