AMINO-ACID RACEMIZATION AND THE PRESERVATION OF ANCIENT DNA

The extent of racemization of aspartic acid, alanine, and leucine prov ides criteria for assessing whether ancient tissue samples contain end ogenous DNA, In samples in which the D/L ratio of aspartic acid exceed s 0.08, ancient DNA sequences could not be retrieved. Paleontological finds from which DNA sequences purportedly millions of years old have been reported show extensive racemization, and the amino acids present are mainly contaminates, An exception is the amino acids in some inse cts preserved in amber.