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Next time

Next time. Quiz on pp. 265-277 Presentations, woo! Some exercises on the reading…. More genetics. Usually things aren’t as simple Single gene traits Two alleles Dominant/recessive. Incomplete dominance. Classic example: flower color in snap dragons C w C w = white C r C r = red

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Next time

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  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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