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Lecture

20.4 Class Notes.docx

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Department
Biology
Course Code
BIO-0013
Professor
Michelle Gaudette

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November 1, 2013 Autosomal dominant • Can disappear in a generation and never reappear in that familial line • Will show up equally in both sexes and won’t skip generations DNA  ▯protein  ▯phenotype Hypercholesterolemia can be argued to be incomplete dominance, but it is called autosomal  dominant because the heterozygotes show the phenotype for high cholesterol  Phenylketonuria (PKU) – a genetic disorder characterized by cognitive defects, eczema, and light  eyes, hair, and skin • Results from a defect in the gene that codes for phenylalanine hydroxylase  • Phenylalanine is toxic to nerve cells, so it needs to be changed into tyrosine  • PKU appears recessive with regards to disease symptoms and plasma concentration of  phenylalanine, but in vitro assays show that heterozygotes have reduced enzyme activity  (incomplete dominance) Huntington’s Disease – a genetic disorder characterized by neurodegeneration and impairment of  motor and cognitive functions • Autosomal dominant  • The basal ganglia (responsible for motor movement) is most affected (by  neurodegeneration)  • Nancy Wexler used genetic mapping to locate the gene on chromosome 4 o Looked for genetic markers that always segregated together with HD   At the time, the best genetic markers were restriction enzyme sites (SNPs  were not discovered yet) o Found that there were genetic marker restriction sites absent in individuals with  HD  o Using this strategy, they mapped the HD disease to a region of about 500,000  bases of DNA  Found an exon in that region (would code for a protein)   This gene, called IT15, which codes for a 3,000 amino acid protein called  huntingtin  The gene has a large number of CAG trinucleo
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