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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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