Incomplete Dominance

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Incomplete Dominance

• Neither allele is completely dominant over the
  other allele.
• The phenotype is heterozygous
• A mixture or blending of the two
• What two colors do you think blended to
  make grey?

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Incomplete DominanceEx Four-o clock
flowers

• Neither Red (R)
• or White (W) is dominant
• When a homozygous red flower (RR)
• mixes with a homozygous white flower (WW),
  the alleles blend in the hybrid (RW) to produce
  pink flowers

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How to Recognize Incomplete Dominance..

1. The offspring is showing a 3rd phenotype (red
   flower, white flower, and pink flower)
2. The trait in the offspring is a blend (mixing) of
   the parental traits (red x white pink)

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Incomplete Dominance Practice Problems

• A cross between a blue blahblah bird and a white
  blahblah bird produces offspring that are silver.
  The color of blahblah birds is determined by
  just two alleles.
• What are the genotypes of the parent blahblah
  birds in the original cross?
• What is/are the genotypes of the silver
  offspring?
• What would be the phenotypic ratios of offspring
  produced by two silver blahblah birds?

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Incomplete Dominance Practice Problems

• In northeast Kansas there is a creature know as a
  wildcat. It comes in three colors, blue, red, and
  purple. This trait is controlled by a single
  locus gene with incomplete dominance. A
  homozygous (BB) individual is blue, a homozygous
  (bb) individual is red, and a heterozygous (Bb)
  individual is purple. What would be the genotypes
  and phenotypes of the offspring if a blue wildcat
  were crossed with a red one?

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Incomplete Dominance Practice Problems

• Coat color in mice is incompletely
  dominant. Yellow and white-colored mice are
  homozygous, while cream-colored mice are
  heterozygous. If two cream-colored mice mate,
  what phenotypic ratio can we expect of their
  offspring?

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Codominance

• Two equally dominant alleles are expressed at the
  same time.
• Heterozygous phenotype will have both phenotypes
  visible

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Codominance

• Ex Short Horn Cattle
• Homozygous red (RR)
• Homozygous white (WW)
• The offspring of will have both red and white
  hairs (RW)
• The offspring are heterozygous and called
  roan

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Codominance Practice Problems

• A cross between a black cat and a tan cat
  produces a tabby pattern (black tan fur
  together). What percent of kittens would have
  tan fur if a tabby cat is crossed with a black
  cat?

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Codominance Practice Problems

• Roan cattle are the heterozygous hybrids of
  a cross between a white bull and a red cow. If a
  roan bull were crossed with a red cow, what would
  be the possible phenotypes of their offspring?

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Codominance
Human Blood types ABO are examples of
codominace. Blood types come from
three different alleles and therefore are
considered a multiple trait allele. The multiple
trait alleles are I , I , and i. I and I
both result in an antigen on the surface of red
blood cells however i is recessive and does not
have an antigen. An antigen stimulates the
production of antibodies.
A
B
A
B
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CodominanceGenotype Phenotype of Blood
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Sickle- Cell Anemia

• Co- dominance
• Caused by an abnormal
• Hemoglobin, the protein that
• red blood cells use to carry
• oxygen
• Normal hemoglobin is (RR)
• Sickle Cell shaped blood cells (SS)
• People who are carriers (heterozygous) for the
  disease there is a mixture of both normal and
  sickle cell (RS)

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Problem Codominance

• Show the cross between an individual with
  sickle-cell anemia and another who is a carrier
  but not sick. Remember RR normal RS
  carrier of sickle cell SS sickle cell
  

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Problem CodominanceBlood Types

• Mrs. Clink is type A and Mr. Clink is type O.
  They have three children named Matthew, Mark, and
  Luke. Mark is type O, Matthew is type A, and
  Luke is type AB. Based on this information
• Mr. Clink must have the genotype ______
• Mrs. Clink must have the genotype ______ because
  ___________ has blood type ______
• Luke cannot be the child of these parents
  because neither parent has the allele _____.

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Problem CodominanceBlood Types

• Two parents think their baby was switched at the
  hospital. Its 1968, so DNA fingerprinting
  technology does not exist yet. The mother has
  blood type O, the father has blood type AB,
  and the baby has blood type B.
• Mothers genotype _______
• Fathers genotype _______
• Babys genotype ______ or ________
• Punnett square showing all possible genotypes for
  children produced by this couple
•   
• Was the baby switched?

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Partner Work ?Find a friend or two and work the
following genetic problems. Have fun and focus
on the task at hand!
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PRACTICE QUESTIONS

• 1. In a certain case a womans blood type
  was tested to be AB. She married and her
  husbands blood type was type A. Their children
  have blood types A, AB, and B. What are the
  genotypes of the parents? What are the genotypic
  ratios of the children?

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• 2. In a certain breed of cow, the gene for red
  fur, R, is codominant with that of white fur, W.
  What would be the phenotypic genotypic ratios
  of the offspring if you breed a red cow and a
  white bull? What would they be if you breed a red
  white cow with a red white bull?

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• 3. A rooster with grey feathers is mated with
  a hen of the same phenotype. Among their
  offspring 15 chicks are grey, 6 are black and 8
  are white.
• a. What is the simplest explanation for the
  inheritance of these colors in chickens?
•  
• b. What offspring would you expect from the
  mating of a grey rooster and a black hen?