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Biology 1001A
Tom Haffie

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Lecture 13Notes Section 173 174 173 The Agents of Microevolution173a Mutations Create New Genetic VariationsA mutation is a heritable change in DNA between 1 gamete in 100 000 and 1 in 1 million will include a new mutation at a particular locus Mutations have been accumulating in biological lineages for billions of years Mutation is a major source of heritable variationFor most animals only mutations in the germ linethe cell lineage that produce gametes are heritable mutations in other cell linages have no direct effect on the next generation In plant mutations may occur in meristem cells which eventually produce flowers as well as nonreproductive structures mutations can be passed on to generationsDeleterious mutations alter an individuals structure functionor behaviour in harmful ways Lethal mutations cause the death of organisms carrying them If a lethal allele is dominant both homozygous and heterozygous carriers suffer for its effect if recessiveit affects only homozygous recessive individuals A mutation that causes death before the individual reproduces is eliminated from the populationNeutral mutationsar neither harmful nor helpful A neutral mutation might even be beneficial later if the environment changes A change in DNA produces an advantageous mutationwhich confers some benefit on an individual that carries it Natural selection may preserve the new allele and even increase its frequency overtime Other agents of microevolution determine its longterm fate173b Gene flow introduces Novel Genetic Variants into populations Organisms or their gametes ex Pollen sometimes move from one population to another Gene flowthe transfer of genes from one population to another through the movement of individuals or their gametes violets the Hardy Weinberg requirementBlue jays foster gene flow amount populations of oaks by carrying acorns from nutbearing trees to their winter supplies which may be as much as 15 kilometers awayGene Flow Blue jays serve as agents of gene flow for oaks when they carry acorns from one oakpopulation to another An uneaten acorn may germinated and contribute to the gene pool of thepopulation into which it was carried
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