Final answer:
Phenotypes like hair color are often the result of polygenic inheritance, where multiple genes determine a single characteristic. This complexity adds to the diversity and variation within species, influencing traits such as skin color and eye color.
Step-by-step explanation:
Some phenotypes, such as hair color, are indeed determined by multiple genes. This is known as polygenic inheritance, a concept where several genes contribute to a particular characteristic. For example, human skin color involves at least three genes, exhibiting the complexity of polygenic traits. Similarly, eye color is another trait influenced by polygenic inheritance, with at least eight genes contributing to the phenotype. Unlike the principles of single-gene inheritance outlined by Mendel, polygenic inheritance involves genes that may function in complementary ways or may be expressed sequentially, adding complexity to the organism's features.
Furthermore, the concept of epistasis shows that genes can influence each other in the expression of phenotypic traits. This means that a single observable characteristic is usually the result of the combined action of multiple genes, each with its own set of alleles. Although an individual can only carry two alleles for each gene, in a population, there are often multiple alleles available, increasing genetic diversity and variation within a species.