Sunday, July 3, 2011

My DNA: My Ancestry

My DNA result is out. I have 64% European and 36% Asian markers, which put me squarely in the Indian subcontinent, somewhat more heterogeneous than the upper caste Brahmins who have roughly 80% or more European and ~20% or less Asian markers on average. This is not surprising, because I am not a Brahmin, but am supposed to be a Vaidya, or, historically a class of Brahmins who were shunned from wed locks with other Brahmins for either reasons of envy, for accepting fees for medical treatment (you see, the Brahmins are supposed only to receive the gifts of gratitude and never a fee for labor) or, more likely, because a wayward Brahmin in my remote ancestry fell for a lower caste boy or girl…

I seem not to have any known marker for any debilitating disease, or even a carrier of any known disease markers. I might be more than average sensitive to Warfarin, a blood thinner given in cases of blood clot diseases or stroke, too much of which could cause bleeding, and knowing this the doctors would be cautious in case they catch me on a stretcher one of these days.

I seem to be a slow metabolizer of caffeine, which explains why I spend so much time in caf├ęs.

So far that is almost all I know that is of significance to my health…the rest are all typical.

The real fun begins when I look at my maternal and paternal ancestries.

Maternal ancestry is provided by the mitochondrial DNA sequence, which rarely changes, and is always contributed by the mother (never the father). Thus my mitochondrial DNA ancestry forms a continuous chain up the line of my mother’s mother’s mother’s mother’s…..mother the Eve in Africa. The same with yours.

The funny thing is that the mitochondrial DNA does change sometimes, but very very rarely. When it does, and the mitochondrion still functions, then the mutated (changed) mitochondrial DNA “diverges” in sequence a little bit from the previous generation, and this changed sequence is then inherited down the line, until all females in that line have all male children, in which case the mitochondrial DNA chain is annihilated. This provides a way to sleuth out the maternal ancestry of the current population on the earth because if my mitochondrial DNA is related to yours then we must have shared the same maternal lineage, and by checking this we can actually chart the migration patterns of groups of people across the globe.

My mitochondrial DNA belongs to the so called haplogroup R6, which is a minor part of a very ancient lineage R that arose in Southeast Asia not long after the first human migrations out of Africa into Asia, who then migrated to Europe, Australia, and the Americas. The haplogroup R arose some 60,000 years ago in Asia, before migration to Europe, Australia and the America; therefore it is found in all these places except in Africa. R6 is a variant of the the original R. R6 is quite rare, and is now found most frequently among some tribes in the mountainous regions of Afghanistan-Pakistan-India border and also in small pockets near Tamil Nadu of southern India and in northern Sri Lanka (source: Metspalu et al. BMC Genetics 2004, 5:26 doi:10.1186/1471-2156-5-26).

Therefore, a woman in my distant ancestry from either the mountains of Kashmir or Afghanistan region, or from Southern India, or one of their common ancestors, must have migrated to the plains of north-eastern Bengal, perhaps over many generations through bearing daughters who migrated slowly, or perhaps it was a single romantic affair that led to one couple eloping together and settling in Bengal, producing a daughter who bore another daughter, and so on. While eye and skin colors are not at all known to be inherited through the mitochondrial DNA—the mitochondrial DNA merely asserts the maternal inheritance line—other genes that do might also have descended from this couple. My maternal grand mother (who was born in north-eastern India in current Assam, in the Dibrugarh area, so far as I recall), from whom I must have inherited my mitochondrial DNA, had bluish green eyes and fair skin, something like what is seen among the tribes of Kashmir region of India, Afghanistan and Pakistan. But the couple might also have come equally likely from southern India, where the incidence of bluish-green eyes is rarer though.

How about my paternal line? This is even more interesting. My paternal line, derived from my Y chromosome, which was given to me by my father (by his father, and so on up to some Adam in Africa), who were all from the Chittagong region of current Bangladesh, belongs to a very rare group H1a*. The haplogroup H, from which H1a* is derived, is mainly restricted to the Indian subcontinent, mostly among the tribes of India and is rarely (~10%) found among the Brahmins, but also its variants are found among the Central Asians including the Afghanis, the Romani gypsies of the Balkans, some central Asians and Iranians, among the Saudis (including their royal families), and in Yemen, and a somewhat distant line in Cambodia/Vietnam. But if one looks more closely at the specific rare variant H1a*, then one finds the closest similarity to a group of "Balkarians" (a Turkish people of the Caucasus mountains), southern Iranians, and Serbians, all of whom contain the mutation M82 in H1a subgroup that is the closest ancestor of H1a* which is mine. Further derivatives of H1a, such as H1a1, H1a2, and H1a3 are found in Nepal, and Southeast Asian countries including Bali, Indonesia and Cambodia, but these are in parallel lineages to that of H1a*, all derived from the common H1a, which likely originated in Northern India or Central Asia.

Whatever I know of my immediate paternal ancestry, my great great grandfather was childless, and adopted a child who was my great grandfather. The only surviving photograph of my great grandfather shows him to be a man of about 50, who was reputed to have had greenish brown eyes, as did my father and as does my daughter.

Was there a lost sailor from Yemen who married a village girl in southern Bengal during his oceanic voyages along the spice route? Or was there a Balkarian soldier in the army of Babur who descended on the Bengal delta and married a woman who produced a son who provided the Y chromosome that ultimately gave rise to my great grandfather?

When I download the entire DNA marker set of my genome (some 700,000 of them) and do principal component analysis (PCA) against all known DNA markers of the world, my DNA markers appear to cluster on the first and second eigen vector spaces right near where the DNA of the indigenous people of central Asia (north of Afghanistan), closest to the Burushos of the Hunza valley of Pakistan-Afghanistan, appear to originate.

These are the stuff of which epic novels are made!

*The above account, as might be expected after a reading, is colored with quite a flight of fancy. To get a slightly more nuanced scientific perspective, read the next entry, My DNA: The Rashomon Factor.


Unknown said...

Very interesting.It reads like a novel... maternal grand mom had bluish green eyes and fair skin and ... great grandfather had greenish brown eyes...and a Balkarian soldier married a village girl...sounds like Rushdie plot...
a romantic novel with a touch of molecular biology :-)

Rajendra Gupta said...

I will wait for the epic story.