Thread: Please explain!
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Old 07-29-2009, 07:24 PM
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Originally Posted by Neezar
Molecular clock? Estimate the date?

And when do they estimate this date to be?

PARIS: The AIDS virus, previously thought to have been transmitted from chimps to humans in the 1930s, may have leapt the species barrier more than a century ago in west-central Africa.

Analysis of tissues preserved by doctors in the colonial-era Belgian Congo shows that the most pervasive strain of the human immunodeficiency virus (HIV) began spreading among humans at some point between 1884 and 1924.

"The diversification of HIV-1 in west-central Africa occurred long before the recognised AIDS pandemic," scientists behind the research announced today in the British science journal Nature.

Molecular clock

AIDS first came to public notice in 1981, when U.S. doctors noted an unusual cluster of deaths among young homosexuals in California and New York. It has since killed at least 25 million people, and 33 million others are living with HIV, the virus that causes AIDS by destroying immune cells.

Epidemiologists trying to date the history of HIV have until now been limited to only one laboratory source that long precedes the detected start of the outbreak. This is a now-legendary blood sample called 'ZR59', which was taken in 1959 from a patient in Leopoldville, now Kinshasa, the capital of the Democratic Republic of Congo (previously Belgian Congo).

HIV is highly mutating virus, with as much as one per cent of its genome diverging per year. This rate of mutation gives rise to a measurement called a 'molecular clock', a timescale at which the HIV deviates from previous strains and from its animal ancestor, the simian immunodeficiency virus (SIV).

New clue

By this calculation, HIV began to spread among humans before 1940, according to ZR59's genes. Now, though, another precious piece of the jigsaw has emerged.

It is a piece of lymph node tissue that was taken for a biopsy from a woman in Kinshasa in 1960 and preserved in a bed of paraffin wax. It was found in the archives of the Anatomy Department at the University of Kinshasa.

As they report in Nature an international team of sleuths pieced together the genetic sequence of the virus the sub-group M of HIV-1 and then compared telltale regions between ZR59 and the second sample, DRC60.

The research was led by Michael Worobey of the Department of Ecology and Evolutionary Biology at the University of Arizona in Tucson, USA.

His team found a significant divergence between the two genetic regions, and calculated that this gap must have taken around 40 years to evolve from a common viral ancestor.
Unfortunately, many of the scientific journals are subscription-based and require a password and can't be linked; however, you could research it at a library. The story linked above describes the research. You could get the actual Nature article at the library.
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