A somatic mutation originates in mitosis and affects a subset of cells. A point mutation alters a single DNA base. Altering the number of bases in a gene may disrupt the reading frame, altering the amino acid sequence of the gene's product. Expanding genes cause some inherited illnesses. Transposable elements move, possibly disrupting a gene's function.
Some mutations are silent.
A mutation in the third position of a degenerate codon can substitute the same amino acid. A mutation in the second codon position can replace an amino acid with a similarly shaped one. A mutation in a nonvital part of a protein may not affect function. The McGraw-Hill Companies. Any use is subject to the Terms of Use and Privacy Policy .