The best explanation for Adam having a short neck despite both of his parents having long necks is that the trait for neck length is not solely controlled by a single dominant allele. Instead, it is likely a polygenic trait influenced by multiple genes, meaning that the inheritance pattern is more complex than a simple dominant-recessive relationship. In this case, Adam may have inherited different combinations of alleles from his parents, resulting in a short neck phenotype. Additionally, environmental factors or mutations could also play a role in determining Adam's neck length.
