Transversions a transition is a substitution of a

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Unformatted text preview: gene. affect one gene Three major types of single-gene mutations • Which type of mutations usually change the protein sequence most? one base changed • Why? • When will an insertion or deletion not cause a frameshift? multiples of 3 wont do much damage alter many codons • When will a substitution most severely affect the protein? when it’s changed to a stop codon/early termination codon Transitions vs. transversions: • A transition is a substitution of a purine for a purine or a pyrimidine for a pyrimidine. • A transversion is a substitution of a purine for a pyrimidine or vice-versa Phenotypic effects of mutations: Base substitutions • Three types of base substitutions: • missense (changes amino acid sequence) • nonsense (changes amino acid to a “stop”) • silent (no change in amino acid sequence) change one base, results in new codon stop codon, nothing after stop codon (no other AA) terminate proteins, protein is nonfunctional if it happens too early does not change AA sequence Phenotypic effects of mutations: Base substitutions does not matter as long as there isnt a huge space between two codons • A neutral mutation is a missense mutation that alters the amino acid sequence of the protein, but does not change its function. • The amino acid may be replaced by another that is similar • The affected amino acid may have little influence on protein function. For Tomorrow: Finish Chapter 18: Mutation and DNA Repair...
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This document was uploaded on 02/25/2014.

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