2 - MUTATIONS Flashcards
- Heritable changes in the nucleotide sequence of a given DNA
- Substitution, deletion or insertion of one or more nucleotides
- Could affect or not a given phenotype
- The major basis of diversity among organisms
- The raw material of evolution
Mutations
Caused (mostly) by
mutagens
UV radiation, ionizing radiation (e.g., gamma rays, X-rays), byproducts (e.g., reactive oxygen species such as superoxides, hydroxyl radicals)
DNA damage
(e.g., base analogs: 5-bromouracil (5-BU), 2-amino-purine; alkylating
agents: ethylmethane sulfonate (EMS); intercalating agents: proflavine, acridine orange, ethidium bromide)
mutagens
(e.g., base excision repair, nucleotide excision repair, mismatch-repair system)
Can be repaired by the body in normal conditions
Classifications of Mutations
Based on nature of occurrence
Based on cell type where it occurs
Based on nature of occurrence
Spontaneous
Induced
arise in the absence of known mutagen
Spontaneous
presence of mutagens or environmental agents
Induced
Based on cell type where it occurs
Somatic
Gametic
originates in mitosis and affects subset of cells
Somatic
originates in meiosis and affects all cells of an individual
Gametic
Gametic
Autosomal
X-linked
change in the sense of information (missense)
Substitution
purine to purine or pyrimidine to pyrimidine
Transition
purine to pyrimidine or vice versa
Transversion
deletion or insertion of one base
Frameshift
change of one letter
point mutation
loss of one letter
deletion (frameshift mutation)
gain of one letter
insertion (frameshift mutation)
mutation changes 1 codon for an amino acid into another codon for that same amino acid
Silent
codon for 1 amino acid is replaced by a codon for another amino acid
Missense