BIOL 142 Lecture Notes - Lecture 11: Phenylketonuria, Intellectual Disability, Quantitative Trait Locus

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7 May 2018
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Biology 142- Lecture 11- Gene Interactions
Extensions of Mendelian Genetics
Most traits are inherited in ways that are more complex than simple Mendelian genetics
patterns
Other examples of inheritance patterns include:
o Incomplete dominance/codominance
o Epistasis
o Polygenic inheritance/quantitative traits
o Complementation
Incomplete dominance/codominance
Incomplete dominance: when heterozygotes have an intermediate phenotype
o Example: a cross of two different color flowers can result in an offspring that is a
blending of the two colors
Codominance: when heterozygotes create a new phenotype that is a combination of the
two alleles
o Example: Blood types are can be codominant, for example, someone could be AB
Penetrance
Penetrance is the proportion of individuals that are carrying a particular variant (allele)
of a gene (genotype) that also expresses an associated trait
Any allele that has 100% penetrance, or close to 100%, is likely a dominant trait
When two alleles have the same penetrance under 60-70%, that is likely an example of
incomplete dominance
When two alleles have 100% penetrance, that is likely codominance
Example: Gg x Gg cross
G
g
G
GG
Gg
g
Gg
gg
G
3 𝑜𝑓𝑓𝑠𝑝𝑟𝑖𝑛𝑔 𝑒𝑥𝑝𝑟𝑒𝑠𝑠 𝑡ℎ𝑒 𝐺 𝑎𝑙𝑙𝑒𝑙𝑒
3 𝑜𝑓𝑓𝑠𝑝𝑟𝑖𝑛𝑔 ℎ𝑎𝑣𝑒 𝑡ℎ𝑒 𝐺 𝑎𝑙𝑙𝑒𝑙𝑒 = 1
100% penetrance
g
1 𝑜𝑓𝑓𝑠𝑝𝑟𝑖𝑛𝑔 𝑒𝑥𝑝𝑟𝑒𝑠𝑠𝑒𝑠 𝑡ℎ𝑒 𝑔 𝑎𝑙𝑙𝑒𝑙𝑒
3 𝑜𝑓𝑓𝑠𝑝𝑟𝑖𝑛𝑔 ℎ𝑎𝑣𝑒 𝑡ℎ𝑒 𝑔 𝑎𝑙𝑙𝑒𝑙𝑒 = 1/3
30% penetrance
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