Figure 2: Effect of Natural Selection Patterns. However, small males can sneak in for furtive copulations with females, along with the alpha males, within the same territory. Therefore, both alpha males that are large and other sneaking males that are small can survive. However, the intermediate-sized males that are unable to overtake alpha males and too big to sneak copulations will have less frequency to survive. Directional selection refers to a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction, while disruptive selection refers to a mode of natural selection in which extreme values for a trait are favored over intermediate values.
Thus, the main difference between directional and disruptive selection is that the directional selection is the selection of a particular phenotype that survives best in the environment while disruptive selection is the selection of extreme phenotypes over the intermediate phenotype.
Moreover, directional selection selects a single phenotype while disruptive selection may select several extreme phenotypes. Hence, this is also a difference between directional and disruptive selection. Another difference between directional and disruptive selection is that directional selection highly reduces the variation within the population while disruptive selection reduces variation only to a certain extent. Directional selection is a mechanism of natural selection responsible for the selection of the phenotype most fitted to the environment over other phenotypes.
It leads to an increase in the allele frequency of the selected phenotype within the population over time. How are directional selection and disruptive selection alike? Angela L. May 24, They both move away from the central "average" phenotype. Explanation: Directional selection is described as the selection for a particular extreme phenotype in the population as opposed to the other phenotypes.
Related questions Why did natural selection favor bipedalism? How does natural selection differ from genetic drift? How does natural selection drive evolution? Mice that carry alleles that make them slightly lighter or slightly darker will stand out against the ground and will more probably die from predation.
Stabilizing selection : Stabilizing selection occurs when the population stabilizes on a particular trait value and genetic diversity decreases. When the environment changes, populations will often undergo directional selection, which selects for phenotypes at one end of the spectrum of existing variation. A classic example of this type of selection is the evolution of the peppered moth in eighteenth- and nineteenth-century England.
Prior to the Industrial Revolution, the moths were predominately light in color, which allowed them to blend in with the light-colored trees and lichens in their environment. As soot began spewing from factories, the trees darkened and the light-colored moths became easier for predatory birds to spot. Directional selection : Directional selection occurs when a single phenotype is favored, causing the allele frequency to continuously shift in one direction.
Over time, the frequency of the melanic form of the moth increased because their darker coloration provided camouflage against the sooty tree; they had a higher survival rate in habitats affected by air pollution. Similarly, the hypothetical mouse population may evolve to take on a different coloration if their forest floor habitat changed. Sometimes natural selection can select for two or more distinct phenotypes that each have their advantages.
In these cases, the intermediate phenotypes are often less fit than their extreme counterparts.
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