9.5 Mutations: Changes in the Genetic Code

produce neither adverse nor helpful changes

neutral mutations

method for detecting mutagenic and potentially carcinogenic agents based upon the genetic alteration of nutritionally defective bacteria

amest test

mutation that counteracts an earlier mutation, resulting in the restoration of the original DNA sequence

back-mutation

insertion or deletion mutation that changes the codon reading frame from the point of the mutation to the final codon; almost always leads to a nonfunctional protein

frameshift mutation

any alteration in DNA that occurs as a consequence of exposure to chemical or physical mutagens

induced mutations

mutations that have a harmful effect on the cell, leading to cell dysfunction or death

lethal mutations

mutation in which a change in the DNA sequence results in a different amino acid being incorporated into a protein, with varying results

missense mutation

any agent that induces genetic mutation; like chemical substances, UV light, radioactivity

mutagen

subspecies of m/o's that has undergone a mutation, causeing expression of a trait that differs from other members of that species

mutant strain

permanent inheritable alteration in the DNA sequence or content of cell

mutation

change that involves the loss, substitution, or addition of one or a few nucleotides

point mutation

mutation that changes in amino-acid-producing codon into a stop codon, leading to premature termination of a protein

nonsense mutation

mutation that, because of the degeneracy of the genetic code, results in a nucleotide change in both the DNA and mRNA but not the resultant amino acid and thus, not the protein

silent mutation

mutation in DNA caused by random mistakes in replication and not known to be influenced by any mutagenic agent; these mutation give rise to an organism's natural, or background, rate of mutation

spontaneous mutation

natural, nonmutated form of a genetic trait

wild type