Complex Patterns of Inheritance
By: Shelby Graff
Multiple Alleles
- Definition: Traits are controlled by more than two alleles for that trait.
- Offspring Phenotype: There are four or more possible phenotypes.
- Examples: Human blood types: Have 3 alleles... Ia, Ib, and i. Ia codes for A blood type, Ib codes for B blood type and i codes for O. This allows for there to be 5 different genotypes. Ia i and Ia Ia genotypes are A blood type phenotype, Ib i and Ib Ib genotypes are B blood type phenotype, Ia and Ib genotype is AB blood type phenotype, and ii is O blood type.
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Incomplete Dominance
- Definition: Neither gene has one allele dominate the other.
- Offspring phenotype: Offspring that are heterozygous express both alleles.
- Examples: Red, pink, and white flowers (RR, Rr, and rr)
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Chicken Color example
Chicken Color example
Chicken Color example
Codominance
- Definition: Both alleles are fully expressed. Neither one is dominant nor recessive.
- Offspring phenotype: Offspring that are heterozygous express both alleles.
- Examples: Red flower crossed with white flower produces a white/red spots. (NOT pink.)
AB blood type. The heterozygous AB genotype produces a new blood type, AB. (Both alleles are expressed.
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Polygenic Traits
- Definition: Trait is controlled by several genes. (The genes may be on the same chromosomes or different ones.)
- Offspring phenotype: Phenotypes are in a wide range. Many different physical traits are possible.
- Examples: Height, skin color, and weight.
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