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Oldest Human Genome Reveals When Our Ancestors Mixed With Neanderthals
sciencehabit writes DNA recovered from a femur bone in Siberia belongs to a man who lived 45,000 years ago, according to a new study. His DNA was so well preserved that scientists were able to sequence his entire genome, making his the oldest complete modern human genome on record. Like present-day Europeans and Asians, the man has about 2% Neanderthal DNA. But his Neanderthal genes are clumped together in long strings, as opposed to chopped up into fragments, indicating that he lived not long after the two groups swapped genetic material. The man likely lived 7000 to 13,000 years after modern humans and Neanderthals mated, dating the mixing to 52,000 to 58,000 years ago, the researchers conclude. That's a much smaller window than the previous best estimate of 37,000 to 86,000 years ago.
The same tests on DNA from another man from the same era and locale but from a different Y-haplogroup (and different mt-haplogroup) might show a completely different proportion of genetic mixing and time to most recent mating. Don't draw too many conclusions from a sample of just one.
Realize that 80% of the human population lives in abject poverty. The "trailer trash" are already above the average human condition.
I don't know if ancient samples are processed differently, but for 'fresh' samples, the DNA gets broken up into small fragments (200-1000 base-pairs long), and then these fragments get sequenced. All bits of the genome have roughly even chance of getting sequenced, and with thousands or millions of copies of each fragment, you normally get reasonably even coverage over the whole genome.
The problem is when you map your sequences back onto a reference genome (ie the currently known chr1, chr2, chrX, etc). The aligning software will have trouble deciding where to place a fragment that is part of a highly repetitive sequence (like centromeres or telomeres) , or is duplicated several/many times (eg large gene families that have large sections of the genes in common, or pseudogenes that look like copies of other genes). In addition, we don't even know the exact sequence for some of these regions, so our reference human genome is contantly being updated (currently up to version 38).
For bioinformatics analysis, sometimes it is easier to sweep some of this under the rug. For example, some people use a reference genome that masks out the centromeres and telomeres (ie our reference sequence just has NNNNNNNNNNNN bases here, instead of As,Cs,Gs and Ts). Otherwise there are databases that list the regions containing repeated sequences or duplicated segments, so you can check any of your findings to make sure they aren't in a suspicious region.
it couldn't be measured if it weren't a distinct genotype. That says nothing about speciation, of course.
My God, it's Full of Source!
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