THE RETRIEVAL OF ANCIENT HUMAN DNA-SEQUENCES

DNA was extracted from similar to 600-year-old human remains found at an archaeological site in the southwestern United States, and mtDNA fr agments were amplified by PCR. When these fragments were sequenced dir ectly, multiple sequences seemed to be present. From three representat ive individuals, DNA fragments of different lengths were quantified an d short overlapping amplification products cloned. When amplifications started from <40 molecules, clones contained several different sequen ces. In contrast, when they were initiated by a few thousand molecules , unambiguous and reproducible results were achieved. These results sh ow that more experimental work than is often applied is necessary to e nsure that DNA sequences amplified from ancient human remains are auth entic. Iu particular, quantitation of the numbers of amplifiable molec ules is a useful tool to determine the role of contaminating contempor ary molecules and PCR errors in amplifications from ancient DNA.