Download Complete dominance

12.2 Notes
When Heredity Follows Different
Rules
Other forms of dominance
I.
II.
III.
Complete
dominance
ex.
Incomplete
dominance
ex.
Codominance
ex.
IV.
Multiple alleles
ex.
V.
Polygenic
inheritance
ex.
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Complete dominance--Inheritance
controlled by either dominant or
recessive alleles
One completely hides the other
Heterozygous and homozygous
dominant have same phenotype
Ex. Tt and TT = tall
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However, not all traits are
controlled by simple
Mendelian principles of
genetics

Incomplete dominance--heterozygous
phenotype is in between the 2
homozygous phenotypes (neither allele is
dominant)
With complete dominance

Old way: if we crossed a red dominant
and a white recessive flower
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Offspring would be red since dominant
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BUT….
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WITH INCOMPLETE DOMINANCE
RR= red flower
WW (R’R’) = white
RW (RR’) = pink flower
R
R
R’
RR’
RR’
R’
RR’
RR’
Cross red with white--The offspring are all pink because that
color is in between 2 red and white
Red (RR)
White (R’R’)
Offspring: All pink flowers
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Codominace--The phenotype of both
homozygous phenotypes are expressed
equally in the heterozygous phenotype
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With complete dominance (old way)
black dominant with white recessive =
black offspring since black is dominant
With incomplete dominance
black with white = gray since gray is
inbetween black and white
BUT…
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WITH CODOMINANCE
BB = black chicken
WW= white chicken BW = checkered
B
B
W
BW
BW
W
BW
BW
Cross black with white chicken--The offspring are all black and
white because that is a combination of both homozygous phenotypes
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Multiple alleles--not all traits are only
controlled by 2 alleles, some traits are
controlled by many different alleles

Ex. Mouse hair color is controlled by
different alleles, black, brown, gray, albino,
etc…
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Polygenic inheritance--Trait that is
controlled by 2 or more different genes
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Ex. skin color, height
Ex. Blood pressure is controlled by genes
for weight, cholesterol, kidney function,
etc…
Review of other forms notes
First step- always make key:
yellow, blue dragons
(figure out options for heterozygous)
Cross blue and yellow (complete dom.)
Cross blue and yellow (incomplete dom.)
Cross blue and yellow (codominance)
Blood Type outline
(day 2- stop here)
I.
II.
An example of III. Chart
Pheno
Geno
Surface
likes
codominace and
multiple alleles
A
Alleles
B
A=
AB
B=
O
o=
IV. Universal donor/ recipient
V.
Rh factor

Blood type
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An example of codominance in humans
Example of multiple alleles, there are more
than 2 alleles for this trait
It is determined by the presence or
absence of carbohydrates (antigens) on
surface of blood cell
Mixing incompatible blood types can cause
cells to clump together and lead to death
Blood types alleles key
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IA = A
IB = B
i = o
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Human Blood Types
Phenotype
Genotype
Blood cell surface
molecules
Type A
IAIA or IAi
A antigens
Type B
IBIB or IBi
B antigens
Type AB
IAIB
A and B antigens
Type O
ii
No antigens
Watch teacher demo on board
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Determine blood types liked by other
blood types
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Alleles IA and IB –are codominant to
each other
Allele i –is recessive to IA and IB
Type O blood—universal donor (has
no antigens so anyone can receive it)
Type AB blood—universal acceptor
(has both A and B antigens so can
take all blood types)
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Cross parent with heterozygous A (IAi)
blood with parent with heterozygous B
blood (IBi)
IA
i
IB
IAIB
IBi
i
IAi
ii
Genotypic ratio
1 IA IB : 1 IA i : 1 IB i : 1 ii
Phenotypic ratio (blood type)—
1 type AB : 1 type A : 1 type B : 1 type
O
Rh Factor
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Describes the presence or absence of
another protein on blood cells
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Rh Positive = have proteins
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Genotypes: Rh+/Rh+ or Rh+/Rh-
Rh Negative = no proteins
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Genotype: Rh-/Rh-
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Cross parent heterozygous for the Rh
factor with another parent who does not
have the Rh factor
Rh+
Rh-
Rh- Rh+/Rh- Rh-/RhRh- Rh+/Rh- Rh-/RhGenotypic ratio
2 Rh+/Rh-: 2 Rh-/Rh-
Phenotypic ratio
2 Rh+: 2 Rh-
Practice dihybrid cross
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Cross TtBb x TtBb
Use FOIL method to set up square
Remember rules of segregation and
independent assortment!
Genotypic and phenotypic ratios
What is probability of having short +
brown eyes?