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Tracing the Genes 3 pages: | 1 | 2 | 3 |

Father's Side of the Family
Dads' DNA can be tracked too. The Y chromosome that all males carry is passed on from father to son with little change, since it doesn't recombine with any of the mother's DNA. Scientists can use the Y chromosome to trace paternal lineages over time. They categorize men into haplogroups based on the presence or absence of different markers found on the Y chromosome. It's a simple test to figure out your haplogroup, using a blood sample or even just a mouth swab. Just like mtDNA, Y chromosomes can hint at where your ancestors originated.

Geneticists have examined the Y chromosomes of Native Americans and the Asians who are presumed to share common ancestors with them. What they see are genetic similarities. Natives of southern Middle Siberia share Y chromosome haplogroups (called M45a and M3) with natives of North, Central, and South America. And other haplogroups (called M45b and RPS4Y-T) native to Chukotka, just across the Bering Strait from Alaska, are shared by indigenous people in North and Central America. These results point to two migrations, and since the people carrying M45a and M3 haplogroups penetrated further into the new world, as far as South America, they probably came over first.

Map of various haplotypes
Y-chromosome data suggest two major male migrations into the new world.

The idea of two separate migrations fits nicely with the two migrations suggested by mtDNA studies. It seems likely that men bearing the M45a and M3 Y chromosome were traveling with women carrying A, C and D mtDNA. Based on the mtDNA dates, this migration probably occurred 20-30,000 years ago. Using similar reasoning, the second wave would have arrived in North America between 9,500 and 7,000 years ago.

Your Great, Great, Great etc Grandfather
Most of these studies collect DNA from people currently living, and then try to figure out where else people with a similar haplotype are alive today. But DNA can be extracted from remains as well. Consider the surprising case of Cheddar Man, a hunter-gatherer who lived in southern England 9,000 years ago. His skeletal remains were found in a cave in 1903. Recently scientists collected DNA samples from people whose families had lived in that area of Somerset for generations, hoping for a match. Using mtDNA, a direct descendant of Cheddar Man was found living only about a mile away from the skeleton's final resting place. Adrian Targett, a history teacher, now holds the honor of having the world's most distant confirmed relative. That's one tall family tree!

Surprising as it may seem, today many people still live in the same regions as their very distant forefathers. Genetic archaeologists bank on this when they assume individuals can be taken to represent a particular local group. In our contemporary world of high-speed travel and far-flung families, the long history of human migrations continues, at an ever-increasing pace. Future mtDNA and Y chromosome hunters will have their work cut out for them if they try to retrace the steps of today's migrants.

3 pages: | 1 | 2 | 3 |

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