Colorectal tumour oncogene sequence traces generated using dideoxysequencing. a: codon 600 valine to glutamic acid change in BRAF. b: codon 12 glycine to alanine change in K-ras. c: the previously unreported double mutation observed in codons 19 and 20 of K-ras resulting in leucine to phenylalanine and threonine to alanine changes at codons 19 and 20 respectively. Additional analyses demonstrated these two base changes to be on the same allele (data not shown). d: codon 13 glycine to aspartic acid change in K-ras.