Question

Now consider heritability in more general terms. Suppose heritability is extremely high for a certain trait in a certain population.

a. First, can the trait be strongly affected by the environment despite the high heritability value? To answer this question, suppose that all the individuals within a certain population have been exposed all their lives to the same level of a critical environmental factor. Will the heritability value reflect the fact that the environment is very important?
b. Second, can the heritability value change if the environment changes? To answer this question, imagine that the critical environmental factor changes such that different individuals are now exposed to different levels of this environmental factor. What happens to the variation in the trait in the whole population? What happens to the heritability value?

Answer 1

Even with high heritability of a trait, environmental factors can strongly influence its expression. A change in environment that affects the levels of a critical environmental factor can lead to a change in heritability, suggesting that both genetics and environment are important for the expression of traits.

Step-by-step explanation:

Heritability is a measure that reflects the proportion of phenotypic variance in a population that is due to genetic variance. When the heritability of a trait is extremely high, it suggests that genetic factors play a large role in the variability of that trait within the population. However, this does not imply that environmental factors do not have an impact. If a population experiences uniform environmental conditions, heritability estimates might not fully reveal the importance of the environment in shaping the trait because the environmental variance is low or nonexistent.

If the environment changes, introducing new variances, such as different levels of a critical environmental factor, the phenotypic variation we observe might shift significantly. The introduction of environmental variability can alter the phenotypic variation, and this can lead to a change in the heritability value. The heritability might decrease if the environment starts contributing more to the phenotypic variance, underscoring that environmental factors can strongly influence the expression of genetic traits.