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Simple Dominance
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The heterozygous expresses the dominant phenotype
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
Incomplete Dominance

The heterozygous expresses less than the homozygous
dominant individual so it seems incomplete
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
1 gene
2 alleles
2 phenotypes
1 gene
2 alleles
3 phenotypes
Codominance

The heterozygous expresses both dominant alleles
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
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1 gene
2 dominant alleles
3 phenotypes

Multiple alleles

3 or more alleles interact to give different phenotypes of the same
gene
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
Blood typing
Polygeneic

2 or more genes interact to give a wide range of different
phenotypes
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
1 gene
3 or more alleles
Multiple phenotypes
2 or more genes
2 alleles
Multiple variations of phenotypes
Hair and eye color
Epistasis
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

A gene controls the expression of a different gene
Rooster combs
Black, Chocolate, Yellow labs

Presence or absence of AB antigens

Type A – A antigen
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
Type B – B antigen
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ii
Because antigens are recognized by the immune system the
right blood must be used for transfusions
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IAIB
Type O – none of the antigens
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IBIB or IBi
Type AB – Both A and B antigen
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
IAIA or IAi
Wrong blood = the immune system will attack it
AB = receive any blood
AB = donate to AB only
O = receive only O
O = donate to anyone
RH factors
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Simple dominance (not the whole story but for our sake)
Have Rh antigen = + (dominant)
Don’t have Rh antigen = – (recessive)

Immune system during pregnancy