Pop. Genetics

Pop. Genetics - Random Genetic Drift in a small population...

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Unformatted text preview: Random Genetic Drift in a small population 1 0.9 0.8 Random Genetic Drift in a very small population 1 0.9 0.8 frequency of A allele frequency of A allele 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 population size: N=100 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 population size: N=10 40 60 generations 80 100 40 60 generations 80 100 Consistently small population. Spotted Owl Population bottleneck. Northern Elephant Seal 1 Population bottleneck. Founder effect. Parent Population Founder Population Non Random Mating 2 Mallards http://www.youtube.com/watch?v=fQI5KUfM2xc Genetic diseases Most mutations are deleterious 3 Mechanisms of Evolutionary Change: MUTATION • Mutation is the source of all novel genetic variation. • Mutation is any change in DNA – mutations occur randomly with respect to what might be adaptively beneficial in a particular selective regime – Most mutations are harmful or neutral, but if conditions change, could become advantageous. Kinds of mutations: Point Mutations 1 • NUCLEOTIDE SUBSTITUTIONS SILENT (synonymous) (no effect on AA sequence) Kinds of mutations 1. Point mutations 2. Chromosomal mutations • Substitutions • Duplications i. silent (synonymous) • Deletions ii. neutral (nonsynonymous) • Inversions iii. missense (nonsynonymous) • Translocations iv. nonsense (nonsynonymous) • Transpositions • Frameshift m utations • basepair i nsertion/deletion NEUTRAL (nonsynonymous) (substituted AA functionally equivalent) MISSENSE (nonsynonymous) (AA change) NONSENSE (nonsynonymous) (unexpected STOP codon) Kinds of mutations: Point Mutations 2 • Frameshift mutations (basepair insertion/deletion) Frameshift mutations Normal Sequence Kinds of mutations: Chromosomal 1 TACAACGTCACCATT AUGUUGCAGUGGUAA meth-phen-gln-trp-STOP DNA SENSE STRAND mRNA POLYPEPTIDE Original chromosome Duplication Paracentric Paracentric Inversion E Frameshift Mutant TACAACGgTCACCATT AUGUUGCcAGUGGUAA meth-phen-pro-val-val DNA SENSE STRAND mRNA POLYPEPTIDE Deletion Locus D is DELETED Paracentric Paracentric inversion (does not include centromere) centromere Pericentric inversion (includes centromere) A Pericentric Inversion EXAMPLE: Tay-Sachs (autosomal recessive neurodegenerative disorder) autosomal recessive Family of insertion & deletion mutants in gene encoding α -subunit of l ysosomal β -hexosaminidase 4 Color Vision and the Vertebrate Eye Rods— light sensitive Cones— detect color Opsin protein in cones— detects certain wavelengths Humans have 3 types Most mammals have only 2 types Birds and fishes have 4 types The bottom line on mutations & evolutionary change • Mutation rates are usually low: 1. each BASE PAIR has about a 1/1010 chance of mutating per replication BASE 1. each LOCUS in a gamete has about a 1/1,000,000 chance of mutating LOCUS each generation • BUT, because of... 1. the large number of genes in a genome that can mutate, 2. chromosome rearrangements that can change many genes simultaneously, and 3. the large numbers of individuals in most populations, • MUTATION CAN GENERATE SUBSTANTIAL VARIATION ACROSS THE GENOME AND IN A POPULATION. 1. Because PER LOCUS mutation rate is low, mutations alone produce only minor deviations from Hardy-Weinberg equilibrium at a locus. 2. If there are large deviations from H-W equilibrium at a particular locus, other evolutionary processes are likely to be acting. 5 ...
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