Which of the following is a type of natural selection for a polygenic trait
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A polygenic trait is a characteristic, such as height or skin color, that is influenced by two or more genes. Because multiple genes are involved, polygenic traits do not follow the patterns of Mendelian inheritance. Many polygenic traits are also influenced by the environment and are called multifactorial. Show
NarrationPolygenic Trait. As we've gotten better at identifying regions of the human genome that are associated with disease and at analyzing complicated genomic data, we've learned that the genetic component of many of the most important health conditions of our time — cancer, heart disease, diabetes — are due to the effects of multiple genes. Hence, polygenic, or many genes. This has been a fascinating area of study, as scientists have begun to study these conditions and realized that the ways that we have of predicting risks for polygenic traits have tremendous potential for improving human health. \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)
 What's fitness? Does this type of fitness have anything to do with natural selection? Usually not. There are countless ways in which an organism can be more "fit," or better adapted to its habitat. And we probably do not know about most of these adaptations. Natural SelectionNatural selection occurs when there are differences in fitness among members of a population. As a result, some individuals pass more genes to the next generation. This causesallele frequencies to change. Sickle Cell and Natural SelectionThe example of sickle-cell anemia is described in the Figure below and Table below. It shows how natural selection can keep a harmful allele in a gene pool. You can also watch a video about natural selection and sickle-cell anemia at this link:http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html. Sickle Cell and Natural Selection. Notice the normal-shaped red blood cell on the left, and the sickle-shaped cell on the right. GenotypePhenotypeFitnessAA100% normal hemoglobinSomewhat reduced fitness because of no resistance to malariaASEnough normal hemoglobin to prevent sickle-cell anemiaHighest fitness because of resistance to malariaSS100% abnormal hemoglobin, causing sickle-cell anemiaGreatly reduced fitness because of sickle-cell anemiaHere’s how natural selection can keep a harmful allele in a gene pool:
The sickle-cell example shows that fitness depends on phenotypes. It also shows that fitness may depend on the environment. What do you think might happen if malaria was eliminated in an African population with a relatively high frequency of the S allele? How might the fitness of the different genotypes change? How might this affect the frequency of the S allele? Natural Selection and Polygenic TraitsSickle-cell trait is controlled by a single gene. Natural selection for polygenic traits is more complex, unless you just look at phenotypes. Three ways that natural selection can affect phenotypes are shown in Figure below. You can also watch an animation comparing the three ways at the link below. bcs.whfreeman.com/thelifewire...hp23/2301s.swf.
Natural selection may affect the distribution of a polygenic trait. These graphs show three ways this can happen. For a review of natural selection and genetic drift, and how they relate to evolution, see http://www.cultureunplugged.com/play/2533/Mechanisms-of-Evolution. Mutation, natural selection, genetic drift and gene flow are discussed at http://www.youtube.com/watch?v=RtIQvkQWTZY (8:45). Summary
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This page titled 5.21: Natural Selection is shared under a CK-12 license and was authored, remixed, and/or curated by CK-12 Foundation via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. Which type of natural selection selects for the average phenotype of a polygenic trait in a population?If natural selection favors an average phenotype by selecting against extreme variation, the population will undergo stabilizing selection.
What are the 3 types of selections that occur on polygenic traits and under what conditions will they occur?Three ways that natural selection can affect the phenotype of polygenic traits includes stabilizing selection, directional selection, and disruptive selection. Stabilizing selection occurs when phenotypes at both extremes of the phenotypic distribution are selected against. This narrows the range of variation.
What are the 3 types of natural selection and examples?Directional selection, stabilizing selection and disruptive selection are three types of natural selection. They are also examples of adaptive evolution. Natural selection is the mechanism of evolution which favors organisms that are better adapted to their environments.
What are the types of natural selection?There are three types of natural selection that can occur in nature, and those three types are as follows:. Directional selection.. Disruptive selection.. Stabilizing selection.. |
