BIOC51H3 Lecture 18: BGYB51H3 Lecture 18 Notes Nov 10

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BGYB51H3 Lecture 18 Notes
-weak selection causes more distribution of traits while strong selection causes less distribution
in traits
-directional selection involves fitness increasing or decreasing with trait value increase
-directional selection decreases variation
-stabilizing selection is most common in stable environments and decreases variation in
phenotype
-stabilizing selection involves intermediate traits favoured
-disruptive selection increases variation in populations and is involved in leading to
divergence through speciation
-quantitative trait selection and the mechanisms of evolution (mutation, gene flow, migration)
cause speciation
-species are evolutionary independent in that mechanisms of evolution produce different
changes in different species
-species consist of interbreeding populations, if sexual, because it shows that genotypes and
phenotypes remain similar through gene flow and migration
-new species formation involves isolation of populations so that there is no gene flow
-mechanisms of evolution must alter traits of the population through divergence
-divergence leads to reproductive isolation which prevents interbreeding or hybrids do poorly
-allopatric speciation is speciation in populations that have been geographically isolated
-sympatric speciation is speciation in the same area but are genetically incompatible, have
different habitats, or differential mate choice
-dispersal and colonization can cause allopatric speciation
-vicariance event is a geological event that splits species distribution and prevents gene flow
between groups
-genetic isolation involves chromosomal mutation that makes descendants genetically
incompatible to parents (e.g. polyploidization)
-polyploidy is common in plants and rare in animals
-polyploid plants can self-fertilize in order to survive
-parthogenetic species and hermaphrodites are polyploidy animals that can self-fertilize
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Document Summary

Weak selection causes more distribution of traits while strong selection causes less distribution in traits. Directional selection involves fitness increasing or decreasing with trait value increase. Stabilizing selection is most common in stable environments and decreases variation in phenotype. Disruptive selection increases variation in populations and is involved in leading to divergence through speciation. Quantitative trait selection and the mechanisms of evolution (mutation, gene flow, migration) cause speciation. Species are evolutionary independent in that mechanisms of evolution produce different changes in different species. Species consist of interbreeding populations, if sexual, because it shows that genotypes and phenotypes remain similar through gene flow and migration. New species formation involves isolation of populations so that there is no gene flow. Mechanisms of evolution must alter traits of the population through divergence. Divergence leads to reproductive isolation which prevents interbreeding or hybrids do poorly. Allopatric speciation is speciation in populations that have been geographically isolated.

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