In selective breeding experiments, it is frequently observed that the strains respond to artificial selection for many generations, with the selected phenotype changing in the desired direction. Often, however, the response to artificial selection reaches a plateau after many generations, and the phenotype no longer changes as it did in past generations. Once a plateau has been reached, is the heritability of the trait very high or is it very low? Explain.

Verified step by step guidance

1. Understand the concept of heritability: Heritability is a measure of how much of the variation in a trait is due to genetic factors versus environmental factors. It is expressed as a proportion ranging from 0 to 1, where higher values indicate greater genetic influence.
2. Recognize the role of genetic variation in artificial selection: Artificial selection relies on genetic variation within a population. If there is sufficient genetic variation, the selected phenotype can continue to change over generations.
3. Analyze the plateau phenomenon: When a plateau is reached in selective breeding experiments, it indicates that the phenotype is no longer changing despite continued selection pressure. This suggests that the genetic variation contributing to the trait has been exhausted.
4. Connect the plateau to heritability: Once the genetic variation is depleted, the heritability of the trait becomes very low because there are no remaining genetic differences to drive further changes in the phenotype. The plateau reflects the limits of genetic potential for the trait under selection.
5. Conclude the explanation: The plateau in response to artificial selection demonstrates that heritability is very low at this stage, as the trait is no longer influenced by genetic factors but may still be affected by environmental factors or other constraints.

Key Concepts

Heritability

Heritability is a measure of how much of the variation in a trait can be attributed to genetic differences among individuals in a population. It is expressed as a value between 0 and 1, where a higher heritability indicates that genetic factors play a larger role in the trait's expression. In the context of selective breeding, high heritability suggests that the trait can be reliably passed on to future generations, while low heritability indicates that environmental factors may have a stronger influence.

Response to Selection

Response to selection refers to the change in the average phenotype of a trait in a population as a result of selective breeding. Initially, when a trait is under selection, the phenotype may change rapidly in the desired direction. However, as breeding continues, the rate of change often slows and may plateau, indicating that the population has reached a limit in the trait's expression due to genetic constraints or diminishing returns from selection.

Genetic Variation

Genetic variation is the diversity in gene frequencies within a population, which is essential for evolution and selective breeding. When a trait reaches a plateau in response to selection, it often indicates that the available genetic variation for that trait has been exhausted. Without sufficient genetic variation, further selection cannot produce additional changes in the phenotype, leading to a stagnation in the response to artificial selection.