Ch. 14_Mutation

Ch. 14_Mutation - Chapter 14 Mutation and DNA Repair Any...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 14 : Mutation and DNA Repair Any change in the DNA sequence of an organism is called a mutation whether a phenotypic change is caused or not. Mutations can be classified in several ways ( Table 14.1 ). a. Spontaneous versus induced mutations. Mutations that occur in the absence of an experimentally applied mutagenic treatment are called spontaneous mutations (even if they are due to naturally occurring known mutagens). In contrast, mutations created by the experimental application of a mutagen are called induced mutations. b. Somatic versus germ-line mutations . Mutations in germ-line cells (eggs/sperms) may be passed on to the next generation. In contrast, mutations in all other cells of a complex organism, like humans, only affect that organism and are not transmitted to the progeny. Such somatic cell mutations may lead to severe disease/death. Cancers are one class of disease caused by somatic mutations. c. Conditional mutations . These genetic changes cause a detectable phenotypic change under one condition (the restrictive condition) but not under another condition (the permissive condition ). A widely used class of conditional mutations is “ heat/cold –sensitive mutations. Cells are able to grow at one temperature but not at another. d. Classification by function - (i) Loss of function mutants . Most mutations are deleterious and often result in a complete loss of function (also called “ null ” or “ knockout ” mutations). These are recessive to the wild type. (ii) Gain of function mutants . The mutant provides a new function, such as a new enzyme activity or production of an enzyme in a tissue or at a developmental stage where normally no activity is present. Gain of function mutants are dominant over the wild type allele. Expression of a wild type gene in an abnormal tissue location is also called ectopic expression” ( Fig. 14.2 ). (iii) Hypo - or hypermorphic mutations - Unlike null mutants, these result in either a reduction or an increase in function of a gene. (iv) Classification based on the nature of the amino acid change in a protein . Due to the degeneracy of the genetic code, a base change sometimes does not change the protein (UUU-> UUC mutation would still result in the amino acid Phe at this position in the protein). Such a mutation is called a silent mutation. Change of one amino acid to another is called a missense mutation ( Figs. 14.3, 14.4 ). Those missense mutations that change one amino acid to a similar amino acid (Leucine to isoleucine or valine, glutamine amino acid codon by a chain termination codon is called a nonsense mutation ( Fig. 14.4 ) (v) Classification based on the type of nucleotide change - Replacement of one nucleotide by a different nucleotide is called a “ base-substitution ” mutation. Replacement of a purine by a purine or a pyrimidine by a pyrimidine is called a transition mutation. Replacement of a purine by a pyrimidine or its reverse is called a
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/29/2011 for the course GENETICS 380 taught by Professor Glodowski during the Spring '08 term at Rutgers.

Page1 / 8

Ch. 14_Mutation - Chapter 14 Mutation and DNA Repair Any...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online