lec10 - 1 D genetic anticipation – occurrence of genetic...

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Lecture 10-environmental effects I. General A. environmental refers to genetic or physical 1. genetic 2. physical B. Can be seen as altered penetrance of expressivity - Why? II. Genetic constitution A. genetic make-up affects expression of traits 1. Often difficult to know precise genetic components that affect phenotypic expression - two exceptions 1. genetic suppression 2. position effect B. Age of onset – expression of mutant phenotype may depend on age of individual 1. Tay-Sachs - lethal defect in lipid metabolism 2. Lesch-Nyhan - lethal defect in HGPRT enzyme 3. Duchenne muscular dystrophy - muscle degeneration 4. Huntington’s chorea - neurodegeneration C. gender - espression of mutant phenotype may depend on gender 1. sex-limited 2. sex-influenced
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Unformatted text preview: 1 D. genetic anticipation – occurrence of genetic disorder at progressively earlier ages in subsequent generations 1. Earlier onset correlates with more severe defect. 2. eg. Myotonic dystrophy III. Physical environment A. conditional mutations 1. Defect only seen under certain conditions 2. Types of conditional mutations a. temperature sensitive i. Himalayan rabbit ii. yeast cell cycle b. nutritional effect i. mutations in enzymes required to synthesize compound ii. human mutations that block metabolism a. phenylketonuria b. galactosemia IV. Acquired characteristics- belief that traits influenced by environment can be passed on to offspring- an example of one way that environment does NOT influence traits 2...
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lec10 - 1 D genetic anticipation – occurrence of genetic...

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