Directional selection occurs when individuals with a certain phenotype are favored over others, causing a shift in the distribution of that trait within a population. As a result, several changes can be observed in the distribution curve for that trait:
1. Shift in the mean: The mean of the trait will gradually shift in the direction favored by selection. For example, if individuals with larger body size are favored, the mean body size of the population will increase over time.
2. Skewing of the curve: The distribution curve will become skewed in the direction of the favored trait. Individuals with the selected trait will become more prevalent, leading to a longer tail on one side of the curve.
3. Reduction in genetic diversity: As individuals with the selected trait have higher fitness and are more likely to survive and reproduce, the genetic variation for that trait will decrease over time. This can lead to a narrowing of the distribution curve.
4. Increase in the frequency of extreme phenotypes: With directional selection, extreme phenotypes that are closer to the selected trait will become more common in the population. This can lead to a higher frequency of individuals with extreme values on one end of the curve.
5. Shift in the mode: The mode, or the peak of the distribution curve, will also shift in the direction favored by selection. This can be a gradual process as more individuals with the selected trait survive and reproduce.
Overall, directional selection leads to a noticeable change in the distribution curve for a trait, as the population adapts to the environmental pressures favoring a particular phenotype.
What changes observed in a distribution curve for a trait effect by directional selection
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