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16-1 Genes & Variation

16-1 Genes & Variation. Darwin’s Ideas Revisited. Darwin Didn’t Know How Heredity Worked Mendel Published In 1860’s Importance Not Realized Until 1900’s Darwin Could Not Explain Source Of Variation How Traits Passed Generation To Generation. Gene Pools. Population

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16-1 Genes & Variation

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  1. 16-1 Genes & Variation

  2. Darwin’s Ideas Revisited • Darwin Didn’t Know How Heredity Worked • Mendel Published In 1860’s • Importance Not Realized Until 1900’s • Darwin Could Not Explain • Source Of Variation • How Traits Passed Generation To Generation

  3. Gene Pools • Population • A Collection Of Individuals Of The Same Species In A Given Area • Gene Pool • The Combined Genetic Information Of All The Members Of A Particular Population

  4. Gene Pools • Relative Frequency • Refers To Alleles • The Number Of Times That Allele Occurs In A Gene Pool • Usually Expressed In Percents

  5. Sources of Genetic Variation Key Concept The Two Main Sources Of Genetic Variation Are Mutations And The Genetic Shuffling That Results From Sexual Reproduction

  6. Mutations • Equals Any Change In The Sequence Of Nucleotides In DNA • Mistakes In Replication • Radiation • Chemicals • Can Affect Small Sections Or Complete Chromosomes

  7. Mutations • Do NOT Always Affect Phenotype • Change From GGA to GGU Still Codes For Glycine • Each Mutation Must Be Judged For Its Affect On An Organisms Fitness.

  8. Gene Shuffling • MOST Inheritable Differences Are The Result Of Gene Shuffling That Occurred In The Parents, During Meiosis (Gamete Production) • 23 pairs of human chromosomes can produce 8.4 Million Different Gene Combinations

  9. Gene Shuffling • Crossing Over • Further Increase Genetic Variation • Sexual 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

  10. Single Gene & Polygenic Traits • Key Concept: • The Number Of Phenotypes Produced For A Given Trait Depends On How Many Genes Control The Trait

  11. Single Gene & Polygenic Traits • Single-Gene Trait • Widow’s Peak • Controlled By One Gene And Is Expressed By Only Two Alleles • Only Two Phenotypes Possible • You Have It (Dominate, ~35%) • Or…..You Don’t

  12. Single Gene & Polygenic Traits • Polygenic Traits • Controlled By More The One Gene • Most Traits Are Polygenic • Genes With Multiple Alleles Are Common

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