Chapter 18: Gene Mutations and DNA Repair
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mutation
inherited change in the DNA sequence of genetic information
somatic mutations
mutation that arises in somatic cells and does not give rise to gametes - mutation is passed to daughter cells, leading to a population of genetically identical cells
germ line mutations
mutation in a germ line cell, ultimately gives rise to gametes - can be passed to future generations, producing offspring that carry the mutation in all their somatic and germ line cells
gene mutation
relatively small DNA lesion that affects a single gene
chromosome mutation
large scale genetic alteration that affects chromosome structure or the number of chromosomes
base substitution
alteration of a single nucleotide in the DNA two types: transition and transversion
transition
type of base substitution mutation - a purine is replaced by a purine or a pyrimidine is replaced by a pyrimidine - more frequent
transversion
type of base substitution mutation - purine is replaced by a pyrimidine or a pyrimidine is replaced by a purine
insertions and deletions
the addition or removal of one or more nucleotide pairs - most common type of mutation - lead to frame shift mutations
frame shift mutations
changes in the reading frame - usually alter all amino acids encoded by the nucleotides following the mutation - can introduce premature stop codons, terminating transcription early
in-frame insertions and in-frame deletions
indels that do not affect the reading frame
expanding nucleotide repeats
mutations in which the number of copies of a set of nucleotides increases - cause of ALS - number of copies increases in succeeding generations - number of copies correlates with severity of the disease or age of onset - can lead to anticipation; diseases become more severe in each generation
strand slippage in trinucleotide repeats
can cause nucleotide repeats - DNA separates and replicates - a hairpin forms during replication, causing part of the template strand to be replicated twice, increasing the number of repeats - new strand separates and replicates - resulting DNA molecule has 5 additional copies of the repeated part
forward mutation
mutation that alters the wild-type phenotype
reverse mutation
changes a mutant phenotype back into the wild type
missense mutation
base substitution that results in a different amino acid in the protein
nonsense mutation
changes a sense codon into a nonsense codon
sense codon
codon that specifies an amino acid
nonsense codon
codon that terminates translation
silent mutation
mutation that changes a codon to a synonymous codon that specifies the same amino acid, altering the DNA sequence without changing the amino acid sequence of the protein - some have phenotypic effects
neutral mutation
missense mutation that alters the amino acid sequence of a protein but does not significantly change its function - occur when one amino acid is replaced by another that is chemically similar or when the affected amino acid has little influence on protein function
loss-of-function mutations
causes the complete or partial absence of normal protein function - alters the structure of the protein so that it no longer works correctly - frequently recessive
gain-of-function mutation
causes the cell to produce a protein or gene product whose function is not normally present - could result in a new gene product - frequently dominant
conditional mutation
mutation expressed only under certain conditions - ex: some affect phenotype only at elevated temperatures