Unit 18- mutations Flashcards
mutations
inherited alterations in the DNA seq
- source of genetic variation
- source of many diseases and disorders
adaptive mutation
- genetic variation critical for evolutionary change that brings about adaptation to new environments
- stressful conditions, where adaptation might be necessary to survive, induce increased mutation in bacteria
causes of mutations
- spontaneous replication error
- spontaneous chem changes
- chemically induced mutations
- radiation
Big categories of mutations
- somatic mutations (all cells derived from that cell with have the mutation)(mitosis)
- germ-line mutations (offspring that came from mutant cell will be completely mutated)(meiosis)
base substitution: transition
the substitution of a purine for a purine or of a pyrimidine for a pyrimidine
base substitution: transversion
substitution of a pyrimidine for a purine or of a purine for a pyrimidine
insertions and deletions: frameshift
affects the reading frame
insertions and deletions: in-frame
does not affect the reading frame
expanding nucleotide repeats
increase the number of copies of a set of nucleotides (fragile sites)(hairpins. 2/3 bases pairing)
forward mutation
wild type —> mutant type
reverse mutation
mutant type —> wild type
missense mutation
amino acid —> diff amino acid
nonsense mutation
sense codon —> stop codon
synonymous mutation
change the base but don’t change amino acid
silent mutation
codon —> synonymous codon (no change in AA seq!)
neutral mutation
no change in function
phenotypic effects of mutations
- loss-of-function mutation
- Gain-of-function mutation
- Lethal mutation
Suppressor mutation
a mutation that hides or suppresses the effect of another mutation
- Intragenic (second mutation at diff site in SAME GENE hides mutation in another site)
- Intergenic (mutation in second gene that hides mutation in first gene)
Factors Affecting Mutation Rates
- Frequency of a change in DNA
- probability that when a change takes place, that it will be repaired
- probability that a mutation will be detected
strand slippage
strand loops out when pairing lots of identical pairs, creating an additional nucleotide if new strand or removal of a nucleotide if template strand
unequal crossing over
causes crossing over and deletions in the same event
radiation
greatly increases mutation rates in all organisms
thymine dimer
two thymine bases dimerized (covalently bonded) and block replication
SOS system in bacteria
allows bacterial cells to bypass the replication block with a mutation prone pathway
