Complex Genetic Principles &

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Complex Genetic Principles Human Genetics
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When Heredity Follows Different Rules
Incomplete Dominance Co-dominance Multiple
Alleles Sex Linkage Polygenic Inheritance
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Incomplete Dominance Codominance
There is no dominant allele, There is no
recessive allele. Both alleles blend to result
in a third phenotype.
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Incomplete Dominance Codominance
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Codominance in Humans Sickle Celled Anemia
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Codominance in Humans Sickle Celled Anemia
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Multiple Alleles - Human Blood Type
Traits that are Controlled by Three or More
Alleles An Individual Has a Combination of Two of
These
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Multiple Alleles - Human Blood Type
Allele A and Allele B are Codominant over Allele
O (recessive)
Blood Type Determined by the Proteins on the
Surface of Red Blood Cells
Type A Protein A
Type B Protein B
Type AB Proteins A B
Type O No Proteins
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Multiple Alleles - Human Blood Type
What are the Genotypes of Each Individual?
Key Red Type A Blue Type B Red/Blue Type
AB White Type O
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Sex Linked Traits
Traits that are Controlled by Genes Found on the
X Chromosome but not the Y Chormosome
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Sex Linked Traits

• Sex Linked Recessive Traits In Human Beings
• Red Green Colorblindness
• Hemophilia

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Sex Linked Traits
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Sex Linked Traits
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Polygenic Inheritance
Genetics of Skin Color
Multiple Gene (Polygenic) Inheritance
Gametes  ABC   ABc   AbC   Abc   aBC   aBc   abC   abc 
ABC 6 5 5 4 5 4 4 3
ABc 5 4 4 3 4 3 3 2
AbC 5 4 4 3 4 3 3 2
Abc 4 3 3 2 3 2 2 1
aBC 5 4 4 3 4 3 3 2
aBc 4 3 3 2 3 2 2 1
abC 4 3 3 2 3 2 2 1
abc 3 2 2 1 2 1 1 0


Table 1. Polygenic inheritance in people showing a cross between two mulatto parents (AaBbCc x AaBbCc). The offspring contain seven different shades of skin color based on the number of capital letters in each genotype.