DNA mutations occur with a high frequency in mammalian cells (due to radiation exposure, metabolic accidents, and exposure to environmental carcinogens). Exceptionally efficient DNA repair mechanisms normally ensure that less than 1:1000 accidental base changes in DNA causes a mutation. Mutations take a variety of forms:
♦ Point mutations (substitution of one base pair of a DNA sequence by another).
♦ Translocations (gene arrangement due to chromosomal breakage and rejoining).
♦ Gene amplification (multiple copies of a gene).
♦ Deletions (loss of genetic material—from a single base to a whole gene).
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