DNA Mutation

mutation

an alteration in DNA sequence

transitions

pyrimidine replaces pyrimidine; purine replaces purine

transversions

purine and pyrimidine are interchanged

missense mutation

results in new triplet code for a different amino acid 

nonsense mutation

results in triplet code for stop codon; translation terminated prematurely

silent mutation

new triplet code still codes for the same amino acid

frameshift mutation

loss or addition of nucleotide causes shift in reading frame; the most deleterious mutation

forward mutation

wild type → mutant type

reverse mutation

mutant type → wild type

suppressor mutation

a mutation that hides or suppresses the effect of another mutation

intragenic suppressor mutation

occurs in the gene containing the mutation being suppressed

intergenic suppressor mutation

occurs in a gene other than the one bearing the original mutation

neutral mutation

any mutation that does not affect an organisms fitness

lethal mutation

interrupt essential processes and results in death

dominant-negative mutation

only one copy of the gene needs to be mutated to cause a disease phenotype

diploid

two sets of chromosomes

haploid

a single chromosome set

somatic cells

the body cells that make up tissues and organs; mutations are not heritable

sex/germ cells

reproductive cells; mutations are heritable

autosomal mutation

occurs within genes located on autosomes

X and Y-linked mutation

occurs within genes located on X and Y chromosomes 

expanding nucleotide repeats

increases the number of copies of a set of nucleotides

spontaneous mutation

changes in nucleotide sequence that occurs naturally

proofreading 

fixing mis-paired bases during DNA synthesis/replication by DNA polymerases 

tautomeric shifts

causes transition mutation in the complementary strand 

tautomers

two molecules with the same molecular formula but different connectivity

depurination

loss of purine, leads to an apurinic site

deamination

loss of an amino group; produces uracil

induced mutation

influenced by extraneous factors

mutagen

natural or artificial agents that induce mutations; changes DNA

intercalacting agents

chemicals that insert themselves between adjacent bases in DNA, causing base-pair distortions and DNA unwinding 

free radicals

chemical species containing one or more unpaired electrons; can alter bases, break phosphodiester bonds, and cause mutation

thymine dimers

when two adjacent thymine bases have become covalently attached to each other

transposable elements

nucleic acid sequence that can move about the genome and change its position within a genome