Archives for posts with tag: DNA

Science wants $20 before I can read the full article. Perhaps I will remember to look at it at the library.

Anyway Popular Archaeology has a nice write-up, http://popular-archaeology.com/issue/12012013/article/before-they-were-native-americans-they-were-beringians 

When one accepts that God didn’t actually say the earth was created just 6,000 years ago, and God doesn’t lie to us in nature, then one can propose good working theories that help explain the awesome diversity we see around us and within ourselves.

Starting around 25,000 years ago, our North American forebears found a fortuitous “green” zone in the Bering Straight, which was then well above sea level, and the area supported short shrubs. The key here is that wood is indispensable in the cold. They used the brush to ignite large bones (with marrow and fat within that would burn and keep the fire going).

This warm zone, that would have been the result of some particular arrangement of ocean currents and weather patterns (and probably the geography), allowed these ancients a workable place to live, but it was also isolated. They didn’t mingle with their progenitors in the rest of Siberia.

Thus, the native Americans  have approximately 10,000 extra years of divergence from those Siberians than we can explain if they just came over the Bering land bridge 15,000 years ago when the ice finally started retreating in our current geological climate epic. (Global warming is good stuff, huh!)

See, this makes good sense, and it gives us a good working understanding of why things are the way we find them today. Read the rest of this entry »

Science Daily carries this story,  http://www.sciencedaily.com/releases/2013/11/131103140259.htm, from University of Nottingham (http://www.nottingham.ac.uk/news/pressreleases/2013/october/life,-but-not-as-we-know-it.aspx), and they reference their paper in Nature, which is of course way too expensive, http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12650.html.

And now for something completely unexpected…

“in some organisms, the replication origins — genetic switches that control DNA replication — are not only unnecessary…”. In other words, they pulled out the chemical switches (machinery) that accomplish DNA duplication, and the things replicated anyway, by an uncontrolled method.

This is basic, but still cool: “Archaea were originally discovered in extreme environments and can survive at very high or very low temperatures, or in highly salty, acidic or alkaline water. They form one of the three distinct branches of life along with bacteria and eukaryotes, which are multi-celled organisms including humans, other animals, plants and fungi. At a genetic level, archaea have been found to be more closely related to eukaryotes, and therefore humans, than to bacteria. The salt-loving Haloferax volcanii being studied by the Nottingham scientists originates from the Dead Sea.” {It seems to me the only thing absolutely essential for life as we have been able to find it so far is liquid water.}

They say, ““The way [these] cells initiate this replication process is to use a form of DNA repair that exists in all of us, but they just hijack this process for a different purpose. By using this mechanism, they kick-start replication at multiple sites around the chromosome at the same time.”” I’m not sure kickstart is the right word. Spontaneous and unhindered (unregulated or without a governing mechanism) seems more in line with what they explain.

From the abstract of the published article, I find this more informative:

DNA replication initiates at defined sites called origins, which serve as binding sites for initiator proteins that recruit the replicative machinery. Origins differ in number and structure across the three domains of life1 and their properties determine the dynamics of chromosome replication. Bacteria and some archaea replicate from single origins, whereas most archaea and all eukaryotes replicate using multiple origins. Initiation mechanisms that rely on homologous recombination operate in some viruses. Here we show that such mechanisms also operate in archaea. We use deep sequencing to study replication in Haloferax volcanii and identify four chromosomal origins of differing activity. Deletion of individual origins results in perturbed replication dynamics and reduced growth. However, a strain lacking all origins has no apparent defects and grows significantly faster than wild type. Origin-less cells initiate replication at dispersed sites rather than at discrete origins and have an absolute requirement for the recombinase RadA, unlike strains lacking individual origins. Our results demonstrate that homologous recombination alone can efficiently initiate the replication of an entire cellular genome. This raises the question of what purpose replication origins serve and why they have evolved. [end quote]

The Nature page includes thumbnails of the figures and a 5MB supplemental data file (Excel spreadsheet).

Awesome.

Albert and Adam rewrite the story of human origins.

From the conclusion:

So, like many discoveries, Perry’s Y chromosome raises more questions than it answers. It will doubtless be fascinating to watch our understanding evolve as the genetics of more individuals, modern and ancient, from more locations are added to the picture.

 

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