Genetics Notes Part Three Beyond Dominant and Recessive Alleles

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Genetics Notes- Part ThreeBeyond Dominant and
Recessive Alleles
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The Principle of Independent Assortment that
genes for different traits segregate
independently during the formation of gametes.
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Dominant or Recessive?

• Some alleles are neither dominant nor recessive,
  and many traits are controlled by multiple
  alleles or multiple genes.
• BB, Bb, bb

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Incomplete Dominance

• The heterozygous phenotype is somewhere in
  between the two homozygous phenotypes.
• Blending
• Ex. Snapdragons and Four Oclock plants red,
  white, pink

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Incomplete Dominance
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Codominance

• Both alleles contribute to the phenotype of the
  organism.
• Ex. Cattle red hair is codominant with the allele
  for white hair. Cattle with both alleles are
  roan (pinkish brown).
• Ex. Chickens with speckled feathers.

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Multiple Alleles

• When genes have 3 or more alleles.
• Ex. Coat color in rabbits.
• Ex. Human blood types.

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Polygenic Traits

• Traits controlled by 2 or more genes.
• Ex. Eye color in fruit flies (3 genes).
• Ex. Human skin color. Wide range of skin colors
  because 4 genes control color.

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Blood Types and Codominance
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Blood type problem

• Charlie Brown and Peppermint Patty got married.
  What possible genotypes will the children have if
  Patty has type A blood (IAIO) and Charlie has
  type AB
• (IAIB) ?

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Sex- Linked Genes

• X Y chromosome determine sex, genes located on
  these are sex-linked.
• Colorblindness, hemophilia, Muscular Dystrophy
  located on the X chromosome.

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X-Linked Alleles

• Males have only one X chromosome.
• All X-linked alleles are expressed.
• Females- both of the recessive alleles have to be
  present to have colorblindness.
• Men pass their X chromosome along to their
  daughters.
• X-linked genes ?father?daughter?son.

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COLORBLINDNESS

• A man with normal XC Y
• vision XCY marries
• a woman with XC
• normal vision XCXc.
• This woman is a Xc
• Carrier of the gene.

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• What is the probability that a daughter will be
  colorblind?
• O chance of colorblind daughters
• What is the probability that a son will be
  colorblind?
• 50 chance of colorblind son