Next, a second tRNA binds by its anticodon to the next mRNA codon, and its amino acid bonds with the methionine the first tRNA brought in. The ribosome moves down the mRNA as the chain grows. Chaperone proteins help fold the polypeptide, and it may be shortened or combined with others. A phenotype that a mutation alters is mutant. A gene can mutate spontaneously, particularly if it contains regions of repetitive DNA sequences.
Mutagens are chemicals or radiation that increase the mutation rate.
A germinal mutation originates in meiosis and affects all cells of an individual. 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.