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Lecture 4

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McGill University
ANTH 203
Michael Bisson

Mechanisms of Evolution Gregor Mendel and Genetics 1865 Experiments in Plant Hybridization Theory of inheritance Ignored for 35 years because most biologists couldn't understand probability statistics Experiments with peas Genes Segment of chromosomes that determine traits Have alternate forms that produce different effects, called alleles Dominant allele: expressed with combined with another dominant or with a recessive allele Recessive allele: expressed only when combined with another recessive allele Trait Any physical characteristics of an organism Polygenic trait: made up of various genes Genotypes The genetic makeup of an organism Phenotypes Observable traits/features Product of genotype and influences of the environment Homozygous 2 identical alleles Heterozygous 2 different alleles The dominant allele will be expressed in the phenotype Mendel's law of segregation Alleles separate during meiosis Contributes to phenotype variation Each allele is as likely to be passed down as any other Independent assortment of genes Source of variation 1. Mutation Only source of truly new genetic variation Can occur in individual gene, or in entire chromosomes, or structural change (i.e. adding a segment, reversal, etc) Most mutations are neutral 2. Recombination Creation of new genotypes resulting from segregation and the exchange of genetic material between paired chromosomes during meiosis Species Any group of organisms which can interbreed to produce fertile offspring Biological species concept Can be contiguous population or separated into sub-populations Mendelian population A population in which genetic material is actually being exchanged Like sub-population e.g. Dogs Gene pool All of the genes in a Mendelian population Polymorphic More than one allele for each trait in a gene pool e.g. Eye color Evolution Defined as a change in the composition of the gene pool over time Bottleneck effect Gene drift Changes in gene frequencies in a population caused by chance Usual
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