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Chapter 17: Evolution of Populations

Chapter 17: Evolution of Populations. Section 17-1: Genes and Variation. Genetics Joins Evolutionary Theory. Heritable traits controlled by genes Changes in genes/chromosomes result in variation Genotype = particular allele combination, along with environmental condition determines phenotype

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Chapter 17: Evolution of Populations

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  1. Chapter 17: Evolution of Populations Section 17-1: Genes and Variation

  2. Genetics Joins Evolutionary Theory • Heritable traits controlled by genes • Changes in genes/chromosomes result in variation • Genotype = particular allele combination, along with environmental condition determines phenotype • Natural selection acts on phenotype – some variations provide advantages, increasing fitness

  3. Populations and Gene Pools • A gene pool consists of all the genes, including all the different alleles, for each gene present in a population • Study relative frequencies of alleles • Evolution is any change in the relative frequency of alleles in the gene pool of a population over time • Natural selection acts on individuals, but populations evolve

  4. Sources of Genetic Variation • There are 3: • Mutations • Genetic recombination • Lateral gene transfer

  5. Mutations • Mutations resulting in changes to phenotype may increase fitness, decrease fitness, or have no affect • Only matter in evolution if they are passed on – must occur in egg or sperm

  6. Genetic Recombination • Occurs during sexual reproduction • Independent assortment produces millions of combinations • Crossing over

  7. Lateral Gene Transfer • Organisms pass genes from one individual to another – not offspring • Can occur between organisms of same or different species • Variation increases in species that picks up “new” genes

  8. Single-Gene Traits • A trait controlled by only one gene • Can have 2 or 3 distinct phenotypes • Most common form of the allele can be dominant or recessive • Just because an allele is dominant does not mean it necessarily appears in greater frequency

  9. Polygenic Traits • Traits controlled by 2 or more genes • Each gene often has 2 or more alleles • Many possible genotypes/phenotypes

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