A transition bias is apparent in all mutated nucleotides. Graphs show the relative frequency with which each nucleotide mutates into each of the other 3. The number of mutations occurring in each nucleotide is shown in parentheses on the x-axis. (A) All mutations. (B) Mutations occurring at the third position of completely redundant codons. Data are from 172 B-CLL sequences from our internal laboratory database and 67 non-B-CLL sequences from the public databases.