When a trait is highly heritable, ________.
a. It is influenced by genes
b. It is not influenced by the environment
c. The variance of the trait in a population can be explained primarily by variance in genotypes
d. A and C are correct
e. A, B, and C are correct

Heritability is a measure of how much of the variation in a trait within a population can be attributed to genetic differences among individuals. It is expressed as a value between 0 and 1, where a higher value indicates a greater genetic influence. Importantly, heritability does not indicate the extent to which a trait is determined by genes in an individual, but rather how much genetic factors contribute to differences in the trait across a population.

Environmental influence refers to the impact of external factors on the expression of traits. While heritable traits are influenced by genetics, environmental factors such as nutrition, climate, and social interactions can also play significant roles. A trait can be highly heritable yet still be affected by the environment, meaning that both genetics and environment contribute to the overall phenotype observed in individuals.

The genotype-phenotype relationship describes how the genetic makeup (genotype) of an organism influences its observable characteristics (phenotype). In the context of heritability, when a trait is said to be highly heritable, it implies that the variance in that trait among individuals in a population can largely be explained by differences in their genotypes, rather than environmental factors. This relationship is crucial for understanding the genetic basis of traits.