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Out of Africa: Human odyssey is traced through DNA
Thursday • February 21, 2008
Diving deep into the human gene pool, scientists in the United States have drawn one of the most detailed maps to date of our evolutionary past.
Their findings are detailed in two studies published Wednesday in the British journal Nature.
One paper reveals that human genetic diversity decreases the further one gets from Africa, the cradle of humanity.
People of African descent are more varied genetically than Middle Easterners, who are in turn more diverse than either Asians or Europeans, the study found.
By the time Homo sapiens migrated to the Americas across the Bering Straits, diversity had dwindled even further.
The other investigation shows that Americans of European descent have more potentially damaging mutations in their DNA than African-Americans, a finding that settles a long-standing debate.
It is now clear, the researchers say, that all persons of European descent, and not just isolated geographic groups, experienced a "genetic bottleneck" -- probably between 30,000 and 100,000 years ago -- as a small, founding population moved into present-day Europe.
As a result, the gene pool in Europe was restricted, and possibly harmful mutations in DNA were handed down over the generations instead of being flushed out of the genome through the evolutionary process of natural selection.
Both papers have important implications for understanding the genetic origin of disease and why some populations -- associated with ethnic groups, geographic locations or both -- seem more at risk from certain disorders than others.
In the first study, a team of international researchers led by Noah Rosenberg of the University of Michigan and Andrew Singleton at the National Institutes of Health (NIH) in Bethesda, Maryland analysed DNA from 485 people in 29 different populations around the world.
They identified and compared 500,000 DNA markers -- slight variations in genetic code in a string of three billion pairs of chemical compounds -- in the human genome.
"Now that we have the technology to look at thousands, or even hundreds of thousands, of genetic markers, we can infer population relationships and ancient migrations at a finer level of resolution than as previously been possible," said Rosenberg.
"Diversity has been eroded through the migration process," he said.
In the second study, Carlos Bustamante of Cornell University in New York state and colleagues sequenced more than 10,000 genes -- nearly half the total human genome -- in 20 Americans of European ancestry, and 15 of African heritage.
They found 40,000 locations with DNA variations in at least one individual, and just under half of those were capable of altering amino acids, meaning they could have potentially far-reaching effects on body chemistry.
The proportion of a subset of "probably damaging" variations in DNA base pairs, called single-nucleotide polymorphisms (SNPs), was 12.1 percent for African-Americans and 15.9 percent for Americans of European descent.
Future investigations should reveal whether other populations went through a similar "bottleneck" as they moved further from Africa, leaving deleterious variants that remain in the DNA today.
In an interview with AFP, Bustamante said his findings opened up new paths for understanding inherited disease but could not be used to predict health outcomes for individuals alive today.
Genomics is such a young science that far more work is needed to comprehend the genetic sources of disease and to map individual genetic codes, he said.
"The results of this study suggest that everybody carries in their genome hundreds of mutations that are disrupting protein structure," he said.
"But in order to correlate them with disease you need to compare sequenced proteins from individuals with and without the disease in order to correlate them with specific mutations." — AFP
Copyright MediaCorp Press Ltd. All rights reserved.
Posts: 2007 | From: Washington State | Registered: Oct 2006
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We had a thread like this earlier. Its interesting to note that even as some people make claims of african *inferiority* and jump on every claim or scientific study they can to validate it (such as on racist "scientific" blogs) studies like this myseteriously go unnoticed and they are eerily quiet.
if the evidence it to be taken it would appear more likely that *the opposite* is true if anything. Ofcourse they would'nt *like* that would they?
Posts: 426 | From: Cali-for-nia | Registered: Jan 2006
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MTDNA AND THE ORIGIN OF CAUCASIANS: IDENTIFICATION OF ANCIENT CAUCASIAN-SPECIFIC HAPLOGROUPS, ONE OF WHICH IS PRONE TO A RECURRENT SOMATIC DUPLICATION IN THE D-LOOP REGION.
mtDNA sequence variation was examined in 175 Caucasians from the United States and Canada by PCR amplification and high-resolution restriction-endonuclease analysis. The majority of the Caucasian mtDNAs were subsumed within four mtDNA lineages (haplogroups) defined by mutations that are rarely seen in Africans and Mongoloids. The sequence divergence of these haplogroups indicates that they arose early in Caucasian radiation and gave raise to modern European mtDNAs. Although ancient, none of these haplogroups is old enough to be compatible with a Neanderthal origin, suggesting that Homo sapiens sapiens displaced H. s. neanderthaliensis, rather than mixed with it. The mtDNAs of one of these haplogroups have a unique homoplasmic insertion between nucleotide pair (np) 573 and np 574, within the D-loop control region. This insertion makes these mtDNAs prone to a somatic mutation that duplicates a 270-bp portion of the D-loop region between np 309 and np 572. This finding suggests that certain nonpathogenic mtDNA mutations could predispose individuals to mtDNA rearrangements.
-------------------- Without data you are just another person with an opinion - Deming Posts: 12143 | From: When you have eliminated the impossible, whatever remains, however improbable | Registered: Jun 2007
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Whole-mtDNA genome sequence analysis of ancient African lineages
Studies of human mitochondrial (mt) DNA genomes demonstrate that the root of the human phylogenetic tree occurs in Africa. Although 2 mtDNA lineages with an African origin (haplogroups M and N) were the progenitors of all non-African haplogroups, macrohaplogroup L (including haplogroups L0-L6) is limited to sub-Saharan Africa. Several L haplogroup lineages occur most frequently in eastern Africa (e.g., L0a, L0f, L5, and L3g), but some are specific to certain ethnic groups, such as haplogroup lineages L0d and L0k that previously have been found nearly exclusively among southern African "click" speakers. Few studies have included multiple mtDNA genome samples belonging to haplogroups that occur in eastern and southern Africa but are rare or absent elsewhere. This lack of sampling in eastern Africa makes it difficult to infer relationships among mtDNA haplogroups or to examine events that occurred early in human history. We sequenced 62 complete mtDNA genomes of ethnically diverse Tanzanians, southern African Khoisan speakers, and Bakola Pygmies and compared them with a global pool of 226 mtDNA genomes. From these, we infer phylogenetic relationships amongst mtDNA haplogroups and estimate the time to most recent common ancestor (TMRCA) for haplogroup lineages. These data suggest that Tanzanians have high genetic diversity and possess ancient mtDNA haplogroups, some of which are either rare (L0d and L5) or absent (L0f) in other regions of Africa. We propose that a large and diverse human population has persisted in eastern Africa and that eastern Africa may have been an ancient source of dispersion of modern humans both within and outside of Africa.
----- No wonder the AE were so variable but always Black African
Posts: 12143 | From: When you have eliminated the impossible, whatever remains, however improbable | Registered: Jun 2007
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