Which is an example of an environmental factor influencing genetic trait expression in humans?

The example highlighting that serious complications from PKU (Phenylketonuria) can be avoided with a low-phenylalanine diet demonstrates how an environmental factor can influence the expression of a genetic trait. PKU is a genetic disorder caused by a mutation in the gene responsible for breaking down phenylalanine, an amino acid found in many protein-containing foods. If individuals with PKU consume phenylalanine, the accumulation can lead to severe neurological issues. However, by adhering to a low-phenylalanine diet, they can prevent the development of these serious complications, illustrating that environmental factors—such as diet—can significantly impact the manifestation of genetic traits and conditions.

This interaction between genetic predisposition and environmental management emphasizes that the expression of traits can be modulated by lifestyle and environmental choices, which are crucial for understanding human genetics and health.