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This comprehensive overview delves into the complexities of genetics, addressing key concepts such as single-gene traits, dominance, incomplete dominance, and codominance. Classic examples, including flower color in snapdragons and blood types, illustrate these principles. The discussion extends to sex-linked traits like color blindness and explores the impact of multiple alleles, polygenic inheritance, and pleiotropy on phenotypes. It highlights how traits can interact with the environment and the significance of independent assortment and genetic linkage in inheritance patterns.

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Presentation Transcript

  1. Next time • Quiz on pp. 265-277 • Presentations, woo! • Some exercises on the reading…

  2. More genetics • Usually things aren’t as simple • Single gene traits • Two alleles • Dominant/recessive

  3. Incomplete dominance • Classic example: flower color in snap dragons • CwCw = white • CrCr = red • CwCr = pink • The heterozygote is a mix of the two homozygote phenotypes

  4. Codominance • Heterozygotes show both phenotypes, not a mix • Like in Sickle-cell anemia • Sickle-shaped cells • Normal-shaped cells • Like Chicken feather color • Black + white = black AND white feathers

  5. Codominance • Another excellent example is blood types • A, B, and O • (also rh factor = +/-) • Each person can have two alleles– A,B, or O

  6. Blood types • These genes code for surface proteins on red blood cells • Recognition by immune system • AA, AB/BA, BB, Ao/oA, Bo/oB = A, AB, B, O • Also an example of multiple alleles…

  7. Sex-linked traits • Genes inherited on the X chromosome behave differently • Color blindness: recessive trait on the X chromosome • Punnet squares

  8. Phenotype • Genotype x Environment • E.g. Siamese cats • Running speed • Skin color • Etc…

  9. Multigene traits • Anything with continuous variation • Like height, skin color in humans • Like flower size in dandelions, protein content in corn • These traits are affected by many genes, each of which has many possible alleles • Polygenic inheritance

  10. Pleiotropy • One gene can affect many traits • This may be true of almost ALL genes • E.g. the SRY gene on the Y chromosome • One gene makes testes instead of ovaries, affects the rest of the child’s development • Influences MANY other genes

  11. Working with multiple genes • Back to Mendel’s peas • Purple vs. White flowers • Green vs. Yellow peas • Independent assortment • Meiosis review… • Punnet Square (dihybrid cross)

  12. Linkage • Sometimes independent assortment doesn’t work – genes are inherited together • Why?

  13. Linkage • If genes are near each other on the same chromosome, they will probably stay together during meiosis • Like red hair and freckles

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