Final answer:
A polygenic trait is an observable characteristic that is influenced by multiple genes, resulting in a continuous variation of phenotypes. These traits do not follow simple dominant or recessive patterns since several genes and their varying alleles collectively influence the outcome. Examples include height, skin color, and eye color in humans.
Step-by-step explanation:
A polygenic trait is a distinguishing characteristic or quality for which the phenotype (appearance) depends on alleles in multiple genes. Unlike a trait controlled by a single gene, polygenic traits are influenced by two or more genes and exhibit a continuous variation, such as height, skin color, or eye color in humans. These genes may have multiple alleles within the population, and the combination of these alleles contributes to the diversity of phenotypes observed.
For example, the alleles an individual inherits construct the individual's genotype, which can be either homozygous or heterozygous. The expression of this genotype determines the phenotype. Phenotypes may exhibit a range of expressions due to the interaction of multiple genes, where the effect of one gene can be either enhanced or diminished by the presence or absence of alleles from another gene.
Even with dominant and recessive alleles, their expression in phenotypes is not as straightforward as with single-gene traits, because multiple genes contribute to the final phenotype, demonstrating the complexity of genetic inheritance beyond what Mendel observed in his early experiments with peas.