Advanced Placement (AP) Biology Practice Exam

What is polygenic inheritance?

1. A single gene controls a single trait

2. Multiple genes influence a trait, leading to continuous variation

3. Traits are determined solely by environmental factors

4. Only dominant alleles affect the phenotype

The correct answer is: Multiple genes influence a trait, leading to continuous variation

Polygenic inheritance refers to the situation where multiple genes contribute to the determination of a single trait. This intricate genetic scenario leads to continuous variation in phenotypic traits, such as height, skin color, or weight, rather than discrete categories. Because several genes are involved, each with potentially additive effects, this results in a range of phenotypes that show a bell-shaped distribution when plotted. In essence, the combined action of multiple alleles at different loci significantly influences the expression of a trait, allowing for a wide spectrum of possible outcomes, which is characteristic of many complex traits in biological organisms. This model highlights the complexity of inheritance beyond simple Mendelian concepts, where traits are typically influenced by a single gene.