Lecture 3

Lecture 3 - Next Topic: Genes Within Populations Evolution...

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Unformatted text preview: Next Topic: Genes Within Populations Evolution can result from any process that causes a change in the genetic composition of a population We cannot talk about evolution therefore without considering population genetics the study of the properties of genes in populations. Five Agents of Evolutionary Change 1. Mutation ultimate source of variation 2. Gene flow movement of alleles between populations 3. Non-random mating can affect proportion of homozygotes vs. heterozygotes 4. Genetic drift the effect of chance on small populations 5. Selection some genotypes do better than others in their environment Any of these forces may bring about changes in allele frequencies. Multiple forces can act at once! All completely new genetic variation arises via mutation Mutation (general) = change in the genetic material carried by individual organisms Mutation (detailed) = an error in the replication of a nucleotide sequence, or any other alteration of the genome (except recombination) In a molecular context a gene mutation is an alteration of a DNA sequence, independent from whether or not it has a phenotypic effect Mutations have evolutionary consequences only if they are transmitted to succeeding generations Mutations are considered by most biologists to be errors . Thus, the process of mutation is generally thought to be not an adaptation, but a consequence of un-repaired DNA damage What are the different kinds of DNA mutations ? Synonymous mutations have no effect on the amino acid sequence of the protein, therefore no effect on phenotype and the mutation is hidden from selection Non-synonymous mutations result in an amino acid change, this change may have little or no effect on the function of the protein, and thus little phenotypic effect, or there may be substantial functional and phenotypic effects Mutations can have phenotypic effects if they occur in protein-coding regions However, even in this case, many mutations will not have phenotypic effects. Why? Redundancy of genetic code (remember neutral theory) Synonymous (silent) mutations have no effect on the amino acid sequence of the protein, therefore no effect on phenotype and the mutation is hidden from selection Non-synonymous mutations result in an amino acid change, this change may have little or no effect on the function of the protein, and thus little phenotypic effect, or there may be substantial functional and phenotypic effects Mutations can have phenotypic effects if they occur in protein-coding regions However, even in this case, many mutations will not have phenotypic effects. Why? Redundancy of genetic code (remember neutral theory) Synonymous (silent) mutations have no effect on the amino acid sequence of the protein, therefore no effect on phenotype and the mutation is hidden from selection Non-synonymous mutations result in an amino acid change, this change may have little or no effect on the function of the protein, and thus little phenotypic effect, or there may be...
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This note was uploaded on 02/13/2011 for the course BIO 124 taught by Professor Dr.duran during the Winter '11 term at Drexel.

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Lecture 3 - Next Topic: Genes Within Populations Evolution...

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