Other Free Encyclopedias » Medicine Encyclopedia » Genetics in Medicine - Part 3 » Molecular Anthropology - Tracing Human Origins Through Genetic Data, Advantages Of Dna Comparisons, Caveats About Sequence Comparisons, Types Of Dna Comparisons

Molecular Anthropology - Neandertal Dna

differences modern humans sequences mitochondrial

DNA can be extracted from some archaeological samples, allowing direct sequencing and comparison with modern DNA. This has so far been possible with specimens up to about 40,000 years old (the dating of such samples is often inexact). DNA is isolated, purified, amplified with the polymerase chain reaction, and sequenced. By this technique, DNA from extinct animals such as the woolly mammoth has been obtained, but not dinosaur DNA, which is millions of years old. The DNA that can be isolated is typically highly fragmented and incomplete, and unsuitable for cloning the whole organism. One application is to analyze the DNA from plant and animal material at camp sites to determine the diet of early humans.

Mitochondrial inheritance is through the mother (circles) only. After only three generations, mitochondrial type D is present in 75 percent of the women in this hypothetical population. Over time, it is quite likely that only one type will be left, simply by chance.

DNA can also be extracted from ancient human remains. As of summer 2002, mitochondrial DNA from two Neandertal skeletons had been extracted, sequenced, and compared. The first was from Germany, and was approximately 35,000 to 70,000 years old. A 378-base pair sequence was determined, and compared to almost one thousand different modern humans. On average, it differed at twenty-seven locations, while modern humans differed among each other at an average of only eight locations. There was some overlap, however, with the least number of differences between Neandertals and modern humans being twenty-two, and the greatest difference noted between modern humans being twenty-three.

The second skeleton was from Russia, and was 29,000 years old. A 345-base pair sequence was determined. It differed at twenty-three locations from a standard modern human sequence, but at only twelve locations compared to the German Neandertal DNA.

Keeping in mind that only two Neandertal sequences have been studied so far, some tentative conclusions have been offered from these data. The amount of difference between the two Neandertal sequences is similar to the amount found between randomly selected modern humans, suggesting that these two specimens, despite being separated by thousands of years, were indeed part of the same lineage.

The amount of difference between the Neandertal skeletal DNA and modern humans suggests that Neandertals were genetically distinctly different from modern humans in their mitochondrial DNA. Were they different enough to constitute a separate species? That is much less clear, and is a source of disagreement among anthropologists. The difference is much less than that between modern humans and chimpanzees, for instance, which suggests that they were not separate species, but it is greater than the differences among subspecies of chimpanzees, which suggests that perhaps they were. Scientists have not been able to compare Neandertal sequences to sequences from anatomically modern humans living at the same time as the Neandertals. It may be that those sequences would be more similar. At present, the relationship of Neandertals to modern humans has still not been conclusively determined.

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