BGYB51H3 Lecture 18 Notes Nov 10

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11 Aug 2010
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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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