Incomplete Dominance, Codominance and Multiple Alleles

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Incomplete Dominance, Codominance and Multiple
Alleles
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Incomplete Dominance

• One allele is not completely dominant over
  another allele
• Uses 2 DIFFERENT letters to represent alleles

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Incomplete Dominance

• Causes a blending of traits
• Example red flower and a white flower are cross
  pollinanted
• The offspring are pink!

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Codominance

• Both alleles contribute to the phenotype
• Causes the two extremes to be seen, not a
  blending
• Uses two different letters to represent alleles
• Example some cows
• Some cows are brown, some are white
• Heterozygous form is brown and white speckled
  not light brown

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Multiple Alleles

• More than two alleles for one gene
• This means there can be more than just two
  variations on one trait
• Example blood types in humans
• A
• AB
• B
• O

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Blood Types

• Type A
• Can have two A alleles (IaIa) or Iai
• Type AB
• One A allele, one B allele (IaIb)
• Also known as the universal receiver

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Blood Types

• Type B
• Two B allelels (IbIb) or Ibi
• Type O
• Must have two O alleles (ii)
• Also known as the universal donor

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Blood Types
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Blood Type Problems

• A man with type A blood marries a woman with type
  A blood. They have a baby with type O blood.
  What are the genotypes of the father, mother and
  baby?

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More Blood Typing Problems

• A man with type B blood marries a woman with type
  A blood. Each of their 6 children have type AB
  blood. What are the genotypes of the father,
  mother and children?
• A man with type A blood marries a woman with type
  B blood. They have one child with type O blood.
  What other possible genotypes could their future
  children have?
• A man with type AB blood marries a woman with
  type AB blood. What is the probability that
  their first child will have type O blood?