Generating Variation: Mutation Lectures

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University of Toronto Scarborough
Biological Sciences
Maydianne Andrade

BIOB51Fall2011 Generating Variation Mutation LectureGenetic Variation and Selectiono After a period of strong natural selectionnatural selection is expected to reduce the heritable variation in populations because it removes the unfavourable traitso Evolution cannot occur without heritable variationo Historical viewnatural selection eliminates most variation in populations so little variation is present in the current populations since natural selection has always been acting on populationso But we also know that mutation is constantly creating new variantsdoes mutation then keep up with natural selection so populations are not so not varied afterall o Gene section of DNA that codes for a distinct RNA or protein producto Locus location of a gene on a chromosomeo Alleles versions of the gene that differ in their base sequence o Mutations are changes in the base sequence of DNAo There are 2 ways to measure genetic variation through polymorphism and mean Heterozygosity H o Polymorphismfraction of genes in a population with at least 2 alleleso Mean Heterozygosity Hmeanof individuals heterozygous per locus OR fraction of genes that are heterozygous in genotype of average persono Example There is Loci A and B in a population which both have 2 alleles therefore polymorphism is 100 On the other hand there are 3 possibilities for each individualAABB AABb and aabbmean heterozygosity is 132 because 1 in 3 posibilities include heterozygous genotypes and there are 2 loci therefore you must divide by 2o Based on allozyme electrophoresiselectrophoretic analysis of variation in enzymes H415 of loci o While 3350 of enzyme loci are polymorphico It is more accurate to examine gene
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