Codominance

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Codominance

• When there are at least 2 usually 3 alleles that
  influence a trait.
• 1 is recessive.
• The other 2 are dominant to that allele but not
  to each other.

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Human Blood Types
In the human population, there are 3 major
alleles for the surface protein gene A, B, and O.
A
A and B are dominant to O but not to each other
B
O
Recessive
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Human Blood Types
Genotype Phenotype
AA or AO IAIA or IAi Type A
BB or BO IBIB or IBi Type B
AB IAIB Type AB
OO ii Type O
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Codominance

• Example homozygous male B (IBIB)
• x heterozygous female A (IAi)

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Codominance

• Example male O (ii) x female AB (IAIB)

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Codominance

• In codominance, the alleles are neither dominant,
  nor recessive. Neither allele is masked by the
  other.

Roan Cow Is both white and red
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Chestnut or Red Roan
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Black or Blue Roan
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Palonimo
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Mystery Bull Experiment

• http//tepserver.ucsd.edu/people/Tracee-Parsons/Fi
  nal-genetics-project/mystery-bull.html

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Flav-R-Gro, Inc.

• Through genetic engineering, you and your
  partner, Maisie have developed a new type of
  corn. You have named it WonderCorn.
• It has a tasty flavor of butter and salt.
• The good thing about this new corn is that you do
  not have to add butter and salt to it once it is
  cooked.
• This makes it a much healthier dish.

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You and Maisie suspect that the taste trait is
corn in codominant. To find out, you crossed two
other types of corn a homozygous salty corn (SS)
and a homozygous buttery corn (BB). The
offspring were all WonderCorn. Create the
Punnett Square
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S
S
B
SB
SB
B
SB
SB
What is the genotype of WonderCorn? What percent
of the offspring will have this genotype?
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You were correct. Taste is a codominant
trait. Make a Punnett Square showing a
second-generation cross. (Both parents are
heterozygous) What percent of the offspring
will be WonderCorn?
S
B
S
SS
SB
B
SB
BB
50 will be WonderCorn. 121 Ratio
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The demand for WonderCorn is high. Grovers
Grocery has already ordered 50 bushels and wants
more. You are all out. You are at the beginning
of a new growing season. Would you be better off
using homozygous plants to grow or heterozygous?
Why?
Yummy to my tummy!
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Do the math!

• If a heterozygous cross produces 736 offspring,
  how many will be WonderCorn?

• How many of the 736 offspring will taste salty
  but not buttery?

50 of 736 368
25 of 736 184
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Quiz
Tomorrow