Gene-phene-Tyr+Lec2 - J.L.Marsh Bio 137B Genes & phenotypes...

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Genes & phenotypes 1 BIOCHEMICAL BASIS OF PHENOTYPE 0] Objectives of this lecture Illustrate: Concept of Pathways with many genes 1gene:1enz step-wise reactions the biochemical basis of complementation Biochemical basis of phenotype using tyrosine metabolism Understanding pathway essential to understanding diseases Dominance relationships Hand out tyrosine pathway the link between genetics and genetic disease and cell biology, developmental biology. A.1] Alkaptonuria -Analysis of defective metabolic enzyme was first application of Classical Medical Genetics. - Mendel's paper of 1864 was "rediscovered" (appreciated) in 1900. In 1902 Sir. Archibald Garrod postulated that Mendel's principles could provide and explanation of how alkaptonuria could appear suddenly in families. Alkaptonuria -Urine turns dark (obvious phenotype) -melanin spots in eyes; darkened cartilage in ears - later, increased risk of arthritis; heart attack - subtle, complex, other ways to get same phenotype of heart attack and arthritis - Garrod postulated recessive inheritance of an Inborn Error of metabolism , for sudden appearance - The idea that you could be born with a metabolic deficiency was a novel idea. Prior to that you can imagine what people were saying to prevent the disease. eg. Because the mother ate liver while nursing or the child was born on moonless night!!! how would you explain that??? - Said affected people lacked enzyme to break down homogentisic acid - 56 years later (1958), the Homogentisic Acid Oxidase discovered - Led to 1 GENE - 1 ENZYME hypothesis - Postulated by Beadle & Tatum 1941 - Got Nobel Prize in 1958 for it. - We must modify to 1 gene - 1 polypeptide & even must modify that with alternative splicing etc. A.2] Tyrosinosis illustrates complementation, phenocopy (e.g. vitC- so we need to ask if it is genetic or non-genetic but both can mimic each other) 2 enzymatic steps from Tyr -->POPP-->Homogenistic acid Block in either = buildup of tyr & Tyrosinosis How do we define genes & how do we determine how many genes (steps) are in a pathway to a given phenotype? How do you determine if 2 mutations are in the same gene? Complementation test
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This note was uploaded on 12/13/2011 for the course BIOSCI 137 taught by Professor Staff during the Fall '11 term at UC Irvine.

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Gene-phene-Tyr+Lec2 - J.L.Marsh Bio 137B Genes & phenotypes...

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