Patterns of Selection Lectures

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Biological Sciences
Maydianne Andrade

BIOB51Fall2011 Patterns of Selection Lecture Pattern of Selection o There are 2 broad categoriespatterns that maintain genetic diversity and patterns that reduce genetic diversityPattern of Selection of Mendelian Geneso Frequency dependant selectionfitness of genotype depends on frequency in population selection first favours one allele and then the otherallele frequencies fluctuate around the same constant levelmaintains genetic variation o Negative Frequency Dependence fitness increases as an allele become rare fitness decreases as an allele becomes commonreferred to as the rare phenotype advantageo Heterozygote Superiority overdominanceheterozygotes have the highest fitness therefore their allele frequency is at stable eq at higher frequency than expected under HW o One Allele Favouredoften leads to fixation of favoured allele and loss of the other allele allele is fixed when its frequency is 10the rate of change depends on initial frequency of each allele and dominancethis reduces genetic diversity and it is the expected pattern on deleterious alleleso Heterozygote Inferiority underdominanceoften leads to fixation of one allele and loss of the otherwhich allele is lost depends on initial frequencies and relative fitness of homozygotespattern that maintain genetic diversity among populations but reduces genetic variation within a populationElderflower Orchid Dactylorhiza sambucinaFrequency Dependant Selection Exampleo Come in 2 colours yellow and purpleo Populations include both colours but yellow is somewhat more commono Flowers attract bumblebeesbut they do not offer a reward o Questionhow can 2 distinct deceptive advertisements persist
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