Cell Biology
Natural selection increases the prevalence of heritable traits that improve an organism's chance of surviving and reproducing, and three major types of natural selection are directional selection, stabilizing selection, and disruptive selection. Directional selection occurs when individuals with one extreme phenotype have the highest fitness in the population, resulting in a shift towards that extreme over time. Stabilizing selection favors intermediate phenotypes, leading to a shift towards intermediate values in the population. This form of selection is the most commonly observed as extreme phenotypes are often disadvantageous. Lastly, disruptive selection occurs when intermediate phenotypes are selected against, favoring two extreme phenotypes because both are advantageous. This results in a decrease in the prevalence of intermediate phenotypes over generations.
Lesson Outline
<ul> <li>Three types of natural selection <ul> <li>Directional selection <ul> <li>Selects for one extreme phenotype</li> <li>Average measurement shifts towards extreme</li> </ul> </li> <li>Stabilizing selection <ul> <li>Selects for intermediate phenotypes</li> <li>Average measurement shifts towards intermediate</li> </ul> </li> <li>Disruptive selection <ul> <li>Selects for two extreme phenotypes</li> <li>Intermediate phenotypes become less common</li> </ul> </li> </ul> </li> </ul>
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FAQs
Directional selection occurs when one extreme phenotype is favored over other phenotypes, causing the allele frequency to shift in one direction. Stabilizing selection favors intermediate phenotypes while selecting against extreme phenotypes, maintaining the population's existing traits. Disruptive selection favors extreme phenotypes at the expense of intermediate phenotypes, potentially splitting the population into separate groups.
Extreme phenotypes might be favored over intermediate ones due to certain environmental conditions or changes. In a process known as disruptive selection, extreme phenotypes are more advantageous than intermediate ones because they better equip organisms to survive or reproduce in specific circumstances. This can result in population divergence, where two or more different groups with distinct phenotypes form within the original population.
Stabilizing selection favors intermediate phenotypes, which tend to be the most common within a population, while selecting against extreme phenotypes. As a result, individuals with intermediate traits have higher survival and reproduction rates, leading to a reduction in population variation. This type of selection preserves the status quo in the population, allowing it to maintain adaptations appropriate for their environment without significant changes to their traits.
