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Evolution of PopulationsEvolution of Populations

Genes & VariationGenes & Variation

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Darwin’s Ideas RevisitedDarwin’s Ideas Revisited

• Darwin Didn’t Know How Heredity Darwin Didn’t Know How Heredity WorkedWorked– Mendel Published In 1860’s

• Importance Not Realized Until 1900’s

• Darwin Could Not ExplainDarwin Could Not Explain– Source Of Variation– How Traits Passed Generation To Generation

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Gene PoolsGene Pools

• PopulationPopulation– A Collection Of Individuals Of The Same

Species In A Given Area

• Gene PoolGene Pool– The Combined Genetic Information Of All The

Members Of A Particular Population

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Gene PoolsGene Pools

• Relative FrequencyRelative Frequency– Refers To Alleles– The Number Of Times That Allele Occurs In A

Gene Pool– Usually Expressed In Percents

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Relative FrequencyRelative Frequency

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Sources of Genetic VariationSources of Genetic Variation

Key ConceptKey ConceptThe Two Main Sources Of Genetic Variation Are

MutationsMutations And The Recombination Recombination That Results From Sexual Reproduction

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MutationsMutations

• Equals Any Change In The Sequence Equals Any Change In The Sequence Of Nucleotides In DNAOf Nucleotides In DNA– Mistakes In Replication– Radiation– Chemicals

• Can Affect Small Sections Or Complete Can Affect Small Sections Or Complete ChromosomesChromosomes

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MutationsMutations

• Do NOT Always Affect PhenotypeDo NOT Always Affect Phenotype– Change From GGA to GGU Still Codes For

Glycine– Each Mutation Must Be Judged For Its Effect

On An Organisms Fitness.

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RecombinationRecombination

• MOST Inheritable Differences Are The Result Of RecombinationRecombination That Occurred In The Parents, During Meiosis (Gamete Production)

23 pairs of human chromosomes23 pairs of human chromosomescan producecan produce

8.4 Million Different Gene 8.4 Million Different Gene CombinationsCombinations

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RecombinationRecombination

• Crossing OverCrossing Over– Further Increase Genetic Variation

• Sexual ReproductionSexual Reproduction– Produces Many Phenotypes– Does NOT Change Relative Frequency of

Alleles• You can shuffle a deck of cards but the chance of

pulling an Ace is always 4:52

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Single Gene & Polygenic TraitsSingle Gene & Polygenic Traits

Key ConceptKey Concept:

The Number Of Phenotypes The Number Of Phenotypes Produced For A Given Trait Produced For A Given Trait

Depends On How Many Genes Depends On How Many Genes Control The TraitControl The Trait

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From Wolves to Dogs?From Wolves to Dogs?