Ch6 Evolution and Adaptation.docx

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University of Toronto St. George
Spencer Barrett

BIO120H © Lis| Page 1011 chapter 6: EVOLUTION AND ADAPTATION  THE PHENOTYPE IS THE OUTWARD EXPRESSION OF AN INDIVIDUAL’S GENOTYPE  genotype: the genetic characteristics that determine the structure and functioning of an organism  phenotype: the physical expression of an organism’s genotype in its structure and function; the outward appearance and behaviour of the organism Genetic Variation  allele: one of several alternative forms of a gene  heterozygous: containing two different alleles of a gene  homozygous: containing two identical alleles of a gene  dominant: an allele that masks the expression of another (recessive) allele of the same gene  recessive: referring to an allele whose expression is masked by an alternative (dominant) allele of the same gene Sources of Genetic Variation  mutation: any change in the genotype of an organism occurring at the gene, chromosome, or genome level; usually applied to changes in the sequence of the nucleotides of DNA The Genetic Basis of Continuously Varying Phenotypic Traits  ADAPTATIONS RESULT FROM NATURAL SELECTION ON HERITABLE VARIATION IN TRAITS THAT AFFECT EVOLUTIONARY FITNESS  evolution: change in a population’s gene pool  fitness: the genetic contribution by an individual’s descendants to future generations of fitness its population  natural selection: change in the frequency of genetic traits in a population through differential survival and reproduction of individuals bearing those traits  artificial selection: differential survival or reproduction that results from conscious decisions made by humans concerning desirable phenotypes of domesticated or laboratory animals and crops          ecologists in the field   BIO120H © Li| Page 22011 Stabilizing, Directional, and Disruptive Selection  sstabilizing selection differential survival or reproduction of individuals with a phenotype at one extreme of the population distribution, resulting in an evolutionary shift in the population average toward that phenotype  ddirectional selection differential survival or reproduction of individu
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