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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
Next time
  • Quiz on pp. 265-277
  • Presentations, woo!
  • Some exercises on the reading…
more genetics
More genetics
  • Usually things aren’t as simple
    • Single gene traits
    • Two alleles
    • Dominant/recessive
incomplete dominance
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
codominance
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
codominance1
Codominance
  • Another excellent example is blood types
    • A, B, and O
    • (also rh factor = +/-)
  • Each person can have two alleles– A,B, or O
blood types
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…
sex linked traits
Sex-linked traits
  • Genes inherited on the X chromosome behave differently
    • Color blindness: recessive trait on the X chromosome
    • Punnet squares
phenotype
Phenotype
  • Genotype x Environment
  • E.g. Siamese cats
  • Running speed
  • Skin color
  • Etc…
multigene traits
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
pleiotropy
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
working with multiple genes
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)
linkage
Linkage
  • Sometimes independent assortment doesn’t work – genes are inherited together
  • Why?
linkage1
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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