biology of sex - Naturalselection,sexual...

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Natural selection, sexual  selection, and adaptation  Evolution in Action
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Evolution:  a definition Some heritable traits help an individual to survive or reproduce better than other individuals. These are the traits that will, over time, increase in frequency in the population, causing evolution the genetically based change in a population's traits over time.
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Natural Selection A population experiences natural selection whenever the following four conditions apply: individuals vary in their traits some of these variations are heritable some individuals survive and reproduce better than other individuals differential survival and reproduction ( fitness ) is influenced by the heritable traits of individuals
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Adaptation An adaptation is a heritable trait that increases an individual's fitness in a particular environment relative to individuals lacking that trait. This concept assumes that the ancestors of the bearers of the trait had the trait and it was advantageous to them. Not all traits are adaptive, and even structures that currently function in organisms may be subject to genetic or historical constraints. We must be attentive to claims that particular traits are adaptations and we will turn to this when we discuss human sexual behavior.
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Constraints on Evolution When selection on alleles for one trait causes a correlated but suboptimal change in another trait, the possible evolutionary outcomes are limited. This type of constraint is called genetic correlation. Lack of genetic variation can also constrain evolution, because natural selection can work only on existing variation in a population. Because all traits evolve from previously existing traits, adaptations are constrained by history. This is called historical constraint. For example, why haven’t we evolved wheels?
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Directional selection Directional selection occurs when natural selection increases the frequency of one allele. This type of selection reduces population genetic diversity over time If directional selection continues long enough, the favored alleles eventually reach a frequency of 1.0 (100%) and are said to be fixed ; those alleles that are no longer found in the population are lost . Directional selection has its theoretical and applied origins in domestication of plants and animals
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Directional Selection, based on human priorities, drives phenotypic divergence in dogs.
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Directional Selection, based on human priorities, also drives phenotypic divergence in domesticated plants
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Directional Selection Selection changes the average value of a trait.
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Darwin’s Finch Bill Morphology Long-term research on changes in body size and beak size and shape in medium ground finches found on Isle Daphne Major of the Gal á pagos Islands showed that natural selection resulting from a drought led to an increase in the finch population's average beak depth.
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Stabilizing Selection Stabilizing selection occurs when
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This note was uploaded on 02/17/2011 for the course BIOLOGY 120 taught by Professor Fink during the Winter '11 term at University of Michigan.

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biology of sex - Naturalselection,sexual...

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