Cryptic genes have been defined as phenotypically silent DNA sequences, usu
ally not expressed during the life cycle of a microorganism, but capable of
expression in a few members of a large population by mutation, recombinati
on, insertion processes, or other genetic mechanisms. Recently, the cryptic
ity of several genetic systems has been questioned. It appears that in many
cases cryptic genes are silent only under the experimental conditions anal
ysed and that their expression can be induced in the natural environment. T
herefore, we propose that cryptic genes might not be a peculiar class of un
iquely regulated genes, but rather genes encoding unusual functions. (C) 20
00 Editions scientifiques et medicales Elsevier SAS.