Chapter 18_post_Pt 1

Genetics: A Conceptual Approach

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Chapter 18- Part I Gene Mutations Dr. Ed Otto George Mason University
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Key objectives Distinguish different types of mutations, as characterized by their molecular nature Review factors that affect mutation rates Examine causes of spontaneous and induced mutations (Note: In part II, we’ll discuss cellular pathways that repair mutations in DNA)
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Mutation Mutation = an inherited change in genetic information; the decendants may be cells or organisms
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Importance of Mutations Mutations are the source of all genetic variation, the raw material of evolution Many mutations have detrimental effects and are the source of diseases and disorders The study of mutations has been key to understanding principles of inheritance Studying mutations is also useful for understanding basic biological process - Mutations that disrupt genes provide insights into their function
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Broad Categories of Mutations In multicellular organisms, there are 2 categories of mutations: 1. Somatic mutations - arise in somatic tissues, which do not produce gametes - when a somatic cell with a mutation divides (mitosis), the mutation is passes to daughter cell - the earlier in development a mutation occurs, the larger the clone of cells that inherits the mutation 2. Germline mutations - arise in cells that produce gametes - the mutation is passed to future generations
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Broad Categories of Mutations Mutations can also be divided into chromosomal and gene mutations: 1. Chromosomal mutations - can be observed by looking at chromosomes with a microscope - can affect many genes - includes: chromosomal rearrangements, aneuploidy, and polyploidy (Ch. 9) 2. Gene mutations - affect a single gene - can only be observed at the molecular level (e.g. by DNA sequencing)
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Classifying Mutations Based on the Molecular Nature of the Defect
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Types of Gene Mutations Mutations may be classified based on the molecular nature of the defect 1. Base substitution = alteration of a single nucleotide in DNA - Two types : i) transition- a purine is replaced by a different purine, or a pyrimidine by a different pyrimidine ii) transversion- a purine is replaced by a pyrimidine, or a pyrimidine by a purine - Although # of possible transversions is twice the # of possible transitions, transitions arise more frequently
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Types of Gene Mutations - Base substitution can produce: a. Missense mutation- results in one different amino acid in a protein a. Nonsense mutation- changes a sense codon to a nonsense codon; leads to premature termination a. Silent mutation- new codon created by the mutation encodes the same amino acid sequence
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Types of Gene Mutations 2. Insertion or deletion = addition or removal of one or more nucleotide pairs - occur more frequently than base substitutions - when they occur within protein-encoding genes, they can cause a frameshift mutation, which changes the reading frame - Alter all amino acids after the mutation - Generally have a drastic effect on phenotype
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This note was uploaded on 05/06/2010 for the course BIO 311 taught by Professor Otto during the Spring '10 term at George Mason.

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Chapter 18_post_Pt 1 - Chapter 18- Part I Gene Mutations...

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