lecture_23__05 - Natural Selection: All populations of...

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Natural Selection: All populations of organisms change from one generation to the next. Some individuals are better able to survive and reproduce in their environment compared to other individuals, and these individuals pass on their genes to the next generation at a higher frequency. Evolutionary Fitness : the relative contribution an individual makes to subsequent generations depends on both survival and reproduction survival is only important in evolutionary fitness when it contributes to reproduction Relative fitness : the contribution of a particular genotype in comparison to other genotypes at the same locus Example: Suppose we sample 1000 individuals and the number of offspring they leave. Focusing on a specific diallelic locus, we find the following: AA Aa aa 10.5 12.0 12.5 average # of offspring: What is the relative fitness of the three genotypes? AA: 10.5/12.5=0.84 Aa: 12.0/12.5=0.96 (aa is defined as having a fitness of 1)
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all of the above can be considered as polymorphisms : Variations of a particular character within a population; polymorphisms can be defined at many different levels variations at the level of physical appearance example : attractive vs. not attractive tall vs. short variations at the level of proteins or other biochemical characteristics example: disease susceptibility immunocompetence How to measure this variation? many discrete characters can be measured by visual inspection or observation biochemical analysis; assays dependent on the biochemical properties of the protein being measured (example: clotting assay for blood types) Individuals have differential evolutionary fitness depending on their phenotypes variations in phenotype can be at many different levels: variations in ability or behavior example : running speed, fast vs. slow mating behaviors
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Natural selection only acts on genetic variation that already exists. "single nucleotide polymorphisms" genetic variation= any kind of differences in DNA sequence AAGTAGGTAGACCCCAA AAGTAG C TAGACCCCAA AAGTAGGTAGACCCC T A A T GTAGCTAGACCCCAA insertions, deletions, translocations, combinations of the above can natural selection act on a group of genetically identical individuals? Natural selection occurs on the basis of phenotype, but it is the
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This document was uploaded on 09/06/2009.

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lecture_23__05 - Natural Selection: All populations of...

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