The deamination of cytosine and adenine is mutagenic; the deamination of guanine is not. The deamination of cytosine leads to G=C-->A=T point mutation and to G-->A and C-->T transition in the DNA molecule; the deamination of adenine leads to the opposite A-->G and T-->C transition. It is shown that adenine lack could be as mutagenic as adenine deamination and it is also shown schematically that adenine lack through defective adenine synthesis could give rise to a population of genetically abnormal cells incapable of any degree of differentiation, a state perhaps reminiscent of the most acute of leukaemias and the most anaplastic of cancers.