Sun 1 Oct 2006
Bryan Sykes is a pioneer in researching mitochondrial DNA (mtDNA). That is the little extra bits of DNA that are included in mammal cells not within the nucleus. The DNA in the mitochondria is passed down only on the female line, as they are not part of the recombination in sexual reproduction, but are included as part of the egg. Like the amoeba, the mitochondrial DNA only changes due to mutation.
Professor Sykes determined that the 500 base pairs of “junk” mitochondrial DNA mutates slowly and at a pretty constant rate, so he figured that by comparing the “junk” bits of DNA he could figure out if your mother’s mother’s mother’s mother is the same as mine. Well surprisingly enough, those of us of European decent have only seven mitochondrial mothers, and from anywhere in the world only thirty three.
It is believed that the mitochondria may have been independent prokaryotic cells that were absorbed into eukaryotic cells and were not digested, but formed a symbiotic relationship internal to the cell. The mitochondria play a critical role in extracting energy for the cell to use. For genetic purposes, the important part is that the mtDNA is almost always inherited from the mother, sperm mitochondria being “marked” for distruction.
In Seven Daughters of Eve Bryan Sykes first tells the story of the science of mtDNA genetics. How the mutation rate was determined, and how it was used to determine which humans decended from which groups. For those who remember Thor Heyerdahl and the Kon-Tiki – he showed that it was possible for the Polynesian islands to have been settled by South American Indians who might have ridden balsa rafts to the islands. His exploits showed that it was possible, but did it happen? Through a chance delay in travel, Bryan had the opportunity to get a substantial number of DNA samples from Polynesian islanders. When the mitochondrial DNA of these samples were compared with those from South American natives and also with those from Asia, it became clear that the islands were populated not from South America, but from Asia.
Bryan Sykes further mused on the maternal lineage of European stock. Would it be composed of many different ancestral “mothers” or would he find that there are relatively few “mothers”. After collecting and sequencing many samples of mtDNA from all over Europe the comparison showed that all Europeans decend from seven maternal lines.
In addition to determining that there were seven, the distribution of mutations provides a good relative indicator of age, and a modestly accurate absolute indicator. Obviously, there are other “mothers” in our genetic stock whose characteristics are mixed in our chromosonal book of DNA, but only seven for Europeans and thirty three for the entire world provided the mtDNA for us all.
Bryan Sykes succeeds in telling a good story of the development of the science of the mtDNA, along with a clear explanation of the anthropological implications of his findings (although heavily eurocentric). He also provides an interesting imagined biography of the women who were the seven daughters of Eve.
This is quite an adventure of discovery, which Professor Sykes has parlayed into a business. If you want to find out which of the mitochondrial mothers from which you decend, his company Oxford Ancestors will sequence your mtDNA sample and report your ancestral mother. Professor Sykes has also been working on the Y chromosome, which is passed exclusively in the patrilineal side. He has recently produced a book on these researches, Adam’s Curse: a Future Without Men.
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