Final answer:
Polygenic traits are indeed a significant contributor to human phenotypic diversity, involving multiple genes and showing a broad spectrum of variability influenced by genetic and environmental factors. Examples include height, skin color, and weight, which often follow a bell-shaped distribution of traits among the population.
Step-by-step explanation:
Yes, it is true that polygenic traits are a major contributor to observable human phenotypic variation. Unlike Mendelian traits, which are influenced by a single gene, polygenic traits are the result of multiple genes working together. These traits include characteristics like height, skin color, and weight, all of which show a wide range of variability and can also be influenced by environmental factors.
Height is an example of a polygenic trait where at least three genes with six alleles are involved. Individuals with different combinations of dominant and recessive alleles for these genes can have a wide range of heights. Similarly, skin color is influenced by the action of at least three genes, and probably more, making it another polygenic trait.
The inheritance of polygenic characteristics often results in a distribution that is bell-shaped, indicating that most individuals possess combinations of traits that place them in the middle range. The complexity of this inheritance makes it difficult to predict phenotypes, as they are a result of the interaction of multiple genes and environmental factors. This genetic diversity is crucial for the survival of species, providing a buffer against the effects of environmental changes and diseases.