Deep Ancestry

For most of our genome we receive half of our genes from our father and our mother. Each half represents a shuffled combination of DNA passed down to us from our ancestors. This recombination process makes it difficult to study lines of descent - it creates a mix of everyone who has come before. Fortunately for anthropological geneticists there are parts of the genome that are passed down unshuffled from parent to child. In these segments the genetic code is varied only through occasional mutations - random spelling mistakes in the long sequence of letters that make up our DNA. When these mutations are passed down through the generations they become markers of descent.

The Y chromosome is the sex-determining chromosome in humans. While all other chromosomes are found in matching pairs, it is the mismatch of the Y with its partner, the X chromosome, that determines gender - men have a mismatched pair (Y and X), while women have two X chromosomes. Because the Y does not have a matching chromosome, most of it (the non-recombining region, or NRY) escapes the shuffling process known as recombination that occurs every generation in the rest of our genome. This allows the Y to be passed down directly from father to son, unchanged, from generation to generation.

Unchanged that is, unless a naturally occurring, random, and usually harmless mutation occurs. The mutation, known as a marker, acts as a beacon; it can be mapped through generations because it will be passed down from the man in whom it occurred to his sons, their sons, and every male in his family for thousands of years.
When geneticists identify such a marker, they try to figure out when it first occurred, and in which geographic region of the world. Each marker is essentially the beginning of a new lineage on the family tree of the human race. Tracking the lineages provides a picture of how small tribes of modern humans in Africa tens of thousands of years ago diversified and spread to populate the world.

As a direct descendant of Basil Tosczak (born ca.1820), I submitted a sample of my own DNA for analysis to identify genetic markers in the Y chromosome, which are used to map an individual’s deep ancestry, reaching back as far as 40,000 to 60,000 years. Below are the results from the laboratory analysis of my Y chromosome. The DNA was analyzed for Short Tandem Repeats (STR's) which are repeating segments of my genome that have a high mutation rate. The location on the Y chromosome of each of these markers is depicted in the image, with the number of repeats for each of my STR's presented to the right of the marker. For example, DYS19 is a repeat of TAGA, so here my DNA repeated that sequence 13 times at that location and appears as: DSY19 13. Studying the combination of these STR lengths allows researchers to place the DNA sample in a haplogroup, which reveals the journeys of our ancestors.

The Y chromosome test results identify my Tosczak ancestors as members of haplogroup E3b, a lineage defined by a genetic marker called M35. Today, the E3b line of descent is most heavily represented in Mediterranean populations. Approximately 10 percent of the men in Spain belong to this haplogroup, as do 12 percent of the men in northern Italy, and 13 percent of the men in central and southern Italy. Roughly 20 percent of the men in Sicily belong to this group. In the Balkans and Greece, between 20 to 30 percent of the men belong to E3b, as do nearly 75 percent of the men in North Africa. The haplogroup is rarely found in India or East Asia. Around 10 percent of all European men trace their descent to this line. For example, in Ireland, 3 to 4 percent of the men belong; in England, 4 to 5 percent; Hungary, 7 percent; and Poland, 8 to 9 percent. Nearly 25 percent of Jewish men belong to this haplogroup. This haplogroup is the final destination of a genetic journey that began some 60,000 years ago with an ancient Y chromosome marker called M168.

The very widely dispersed M168 marker can be traced to a single individual "Eurasian Adam." This African man, who lived some 31,000 to 79,000 years ago, is the common ancestor of every non-African person living today. His descendants migrated out of Africa and became the only lineage to survive away from humanity's home continent.

Population growth during the Upper Paleolithic era may have spurred the M168 lineage to seek new hunting grounds for the plains animals crucial to their survival. A period of moist and favorable climate had expanded the ranges of such animals at this time, so these nomadic peoples may have simply followed their food source.
Improved tools and rudimentary art appeared during this same epoch, suggesting significant mental and behavioral changes. These shifts may have been spurred by a genetic mutation that gave Eurasian Adam's descendants a cognitive advantage over other contemporary, but now extinct, human lineages.

M168 gave rise to M174, an ancient African lineage that first appeared in a direct descendant of Eurasian Adam. This lineage likely accompanied M130-bearing populations on their great migration some 50,000 years ago.
M174 is one of two African lineages defined by the presence of the YAP polymorphism—the other is M96.

The origins of M96 are unclear, though geneticists believe that the marker arose in northeast Africa. Further data, such as that collected by international projects currently underway, may shed light on the precise origin of this lineage.

Some 30,000 to 40,000 years ago much of the earth's water was frozen in massive ice sheets. At this time hunters carrying the M96 marker migrated out of Africa and followed expanding grasslands and plentiful herds of game to the Middle East.

These people may have journeyed with members of the more common M89 lineage to which some 90 to 95 percent of all non-Africans today trace their roots. Alternatively, a later, smaller group of M96 bearing people may have undertaken their own migration along the same route previously traveled by M89 peoples.

The man who gave rise to marker M35 was born around 20,000 years ago in the Middle East. His descendants were among the first farmers and helped spread agriculture from the Middle East into the Mediterranean region.
This is where the genetic trail, as I know it today, ends. However, as additional data is collected and analyzed by international projects currently underway, more details will be learned and updated on this site.

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