Lecture06 - BIS101/Engebrecht Lecture06 4/9/10...

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BIS101/Engebrecht Lecture06 4/9/10 Announcements: Review Quiz is due tonight online. I recapped the alleles we discussed yesterday. You should understand dominance vs. recessive, hierarchy of dominance, incomplete dominance, co-dominance, null (loss-of-function) alleles, hypomorphic (leaky) alleles, conditional alleles and recessive lethality. Dominant lethality: This is when an allele causes death in the heterozygote. Usually, such a disease has a delayed onset (otherwise you would never see it). An example is Huntington corea, which appears in the 4 th decade of life (usually after child bearing years). Penetrance and Expressivity: Penetrance refers to the % of individuals with a given genotype that have the phenotype. Most of the traits we have been discussing are fully penetrant, meaning that if you have a given genotype you will exhibit the expected phenotype. However, it is not uncommon, particularly in human disease traits that there is not full penetrance. For example, if the disease is said to be 75% penetrant than only 3/4 with the genotype will exhibit the disease. This is usually a consequence of modifiers, epistatic genes and suppressors (see below) or the environment (remember Diabetes from the first lecture). Expressivity refers to the amount of expression of different genes. This is also due to changes in modifiers, epistatic genes, suppressors and/or environment. Unfortunately, these things make human genetics much more complicated! You do not need to worry about penetrance and expressivity in our problems.
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This note was uploaded on 07/02/2010 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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Lecture06 - BIS101/Engebrecht Lecture06 4/9/10...

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