15BIS101F2013MutatLect15

Lrodriguez 50 molecular mechanism of mutation the

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Unformatted text preview: aries from six to approximately 50. Courtesy, Dr. David Ussery BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 49 Fragile X Syndrome The defect is due to base slippage during replication of multiple CGG repeats. The Repeats in the 6 to 200 range (premutations) appear normal. Males with repeats Repeats appear in this range are called “normal transmitting males” or NTMs. Repeats of 200 and greater show the disease phenotype. and Increase in CpG or the CGG repeat is a target for DNA methylation (5 ’ methyl methyl cytocine) which seems to reduce the expression of the FMR-1 gene. One strand FMR-1 of the repeated region has been shown to form a hairpin structure that blocks DNA synthesis. The best test for fragile X mental retardation is a PCR-based test using primers The flanking the CGG repeats. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 50 Molecular Mechanism of Mutation The Ames Test BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 51 Key Terms: The Ames Test is a simple bacterial assay that allows researchers to quickly screen thousands of chemicals for their potential genotoxicity and carcinogenicity. The test is based on the principles of mutation analysis and bacterial genetics. the Reversion analysis is the study of the frequency, cause and Reversion nature of back mutations. back Wild type bacteria (prototrophs) are mutagenized with well are characterized mutagens and mutant strains are isolated that are incapable of growth on minimal medium. These mutants are called auxotrophs. auxotrophs The risk of a real or potential mutagen can be assessed by The calculating the HERP%: Human Exposure/Rodent Potency HERP%: percentage. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 52 The Ames Test Since World War II, the chemical industry has created more than 200,000 new Since chemicals, many of which have been introduced into the environment. New chemical compounds are being created at a rate of 1,500 to 2,000/year. Many of these compounds are noxious and/or toxic to humans and other animals. Some of these compounds are genotoxic, or capable of damaging the DNA in our genotoxic or chromosomes. We are also now discovering that many compounds, which occur naturally in plant and animal tissues, can also be highly mutagenic. For these reasons researchers have developed methods to monitor the environment for potential genotoxic compounds using rapid, inexpensive, and reliable tests like the Ames test. BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 53 Ames Test Ames Because there is a 90% correlation Because between mutagens and carcinogens muta...
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This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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