NOTES

1
NOTES Complex Inheritance Patterns

• Most human traits have more than 2 or 3 forms.
  Types of inheritance that are more complex than
  simple dominance, incomplete dominance or
  codominance control these traits.

2
Multiple Allelic Inheritance (Multiple Alleles)

• Traits are controlled by 1 gene with more than 2
  alleles
• Ex. The ABO Blood Type System in Humans

• The gene that controls ABO blood type has 3
  alleles
• A Type A blood B Type B blood o Type O
  Blood
• Alleles A and B are codominant and allele o is
  recessive

3
There are 6 possible genotypes and 4 possible
phenotypes

• A A or A o Type A Blood
• B B or B o Type B Blood
• AB Type AB Blood
• o o Type O Blood

4
Blood Cells
5

• There are four basic Blood types
• Type A with A antigens on the red cells and anti
  B antibodies in the plasma.
• Type B with B antigens on the red cells and anti
  A antibodies in the plasma.
• Type AB with both A and B antigens on the red
  cells and no blood type antibodies in the plasma.
  
• Type O with no antigens on the red cells and both
  anti A and anti B antibodies in the plasma

6
Polygenic Inheritance

• Traits are controlled by more than 1 gene
• There are many possible phenotypes
• Ex. Skin color is controlled by at least 3 genes
• A dark skin a light skin
• B dark skin b light skin
• C dark skin c light skin

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• Differences in skin color are largely due to
  differences in the amount of melanin, a dark
  pigment produced by skin cells.
• Each dark skin allele (A, B, C) codes for high
  melanin production
• Each light skin allele (a, b, c) codes for low
  melanin production
• Each dark skin allele (A, B, C) in the genotype
  adds a small but equal amount of pigment to the
  skin

8
Some possible genotypes and phenotypes

• aabbcc very light skin
• AABBCC very dark skin
• AaBbCc medium skin

9
What would a Punnett Square for skin color look
like?

• Cross two medium skin tone parents
• AaBbCc X AaBbCc
• Each parent could produce 8 different possible
  combination to pass on ABC, ABc, AbC, Abc, aBC,
  aBc, abC, or abc

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11
Blood Type Is Polygenic

• Another level of specificity is added to blood
  type by examining the presence or absence of the
  Rh protein
• Each blood type is either positive "" (has the
  Rh protein) or negative "-" (no Rh protein)
• For example, a person whose blood type is "A
  positive" (A ), has both type A and Rh proteins
  on the surface of their red blood cells
• The Rh protein gene has two alleles
• R protein present () r protein absent
  (-)

12
Polygenic Blood Type

• What is the phenotype of a person who has the
  blood type genotype ABRr?
• Type AB
• What is the phenotype of a person who has the
  blood type genotype oorr?
• Type O
• What would be the genotype of a person who is A
• AARR or AoRR or AARr or AoRr

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