Freitag, 25. Februar 2011

Triangulation 2 ( reflections )

My Chinese cousin

Comparing even two identical mitochondrial Full Genome Sequences cannot proof a possible familiar relationship, since the last mutation may have occurred 2 – 5 thousand years ago. Y-chromosomes are mutating faster and can scratch on the timeframe of genealogical interest, but are also not easy to handle possible relationships. Only autosomal comparing can reveal stretches, pointing to a common ancestor. Beside the mere information about the genetic distance, start and endpoints of the predominant smaller HIR’s, “Ancestry Finder” lists all the countries, our grandparent generation comes from plus a possible Ashkenazi heritage.
At first glance almost everybody will have been surprised to find countries listed, no one would have expected as part of his own ancestry. How is it possible with my pure German descent to have a distant cousin with some grandparents from China?
This is a point worth to be focused – and illustrated.
There has been a famous son of my town Cologne in the 17th century – Johann Adam Schall von Bell, whom I would like to abuse as an example in an experiment of thoughts. He was a Jesuit missionary and succeeded in becoming a mandarin of the first class at the Chinese emperors court, named Tang Ruowang. The fundament for this career have been his skills in mathematics, astronomy and his knowledge in the cannonball construction. As a highly gifted young man of sixteen he decided in 1608 to leave Cologne and head for Rome to join the Collegium Germanicum, although the age of entrance was eighteen, but he could successfully convince them.
There are no spouses or love affairs reported, but let us pretend for our experiment, that he had at least two of them. We could imagine, that he left a young German girl pregnant behind in Cologne and later in China had an affair with a noble Chinese woman.
As a possible common ancestor we should have a look, what could become of his genome in two different geographical contexts.
Due to recombination his original genome will be reduced by halves in each generation, but we cannot know, which segments will completely vanish or rest conserved as tiny bits and pieces. In our Chinese simulation we can expect this reduction in the given ratio, as his German contribution functions like a drop in the ocean. After 12/13 generations it will be hard to trace German parts in his Chinese offsprings.
 If we draw the triangle comparing the genomes of Schall von Bells offsprings, we can perceive two phenomenons: at about the same ratio of proportions there should be a slightly different outcome, because recombination not occurs at the same breaking points. The second difference is the important one for me: in the Chinese genepool original segments will vanish regularly and rapidly, but in a regional German genepool there are repeated chances in the course of generations, that segments could accumulate and recombine over and over, thus creating segments, whose real age is unclear, but who should be considered as specific for geographical regions. But this has to be proved!

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