In a 1998 analysis of the E. coli genome, a large number of genes with unknown function were designated names beginning with the letter y, followed by sequentially generated letters without a mnemonic meaning (e.g., ydiO and ydbK). Since being designated, some y-genes have been confirmed to have a function, and assigned a synonym (alternative) name in recognition of this. However, as y-genes are not always re-named after being further characterised, this designation is not a reliable indicator of a gene's significance.