пятница, 20 ноября 2015
We are more closely related to apes, like gorillas and chimpanzees, than we are to monkeys. But even when HIV has passed into human populations from these apes, it has not necessarily turned into a widespread health issue.
HIV originating from apes typically belongs to a type of virus called HIV-1. One is called HIV-1 group O, and human cases are largely confined to west Africa.
In fact, only one form of HIV has spread far and wide after jumping to humans. This version, which probably originated from chimpanzees, is called HIV-1 group M (for "major"). More than 90% of HIV infections belong in group M. Which raises an obvious question: what's so special about HIV-1 group M?
It is not especially infectious, as you might expect. Instead, it seems that this form of HIV simply took advantage of events. "Ecological rather than evolutionary factors drove its rapid spread," says Nuno Faria at the University of Oxford in the UK.
Faria and his colleagues built a family tree of HIV, by looking at a diverse array of HIV genomes collected from about 800 infected people from central Africa.
The very first person to be infected with HIV-1 group M probably picked up the virus in the 1920s
Genomes pick up new mutations at a fairly steady rate, so by comparing two genome sequences and counting the differences they could work out when the two last shared a common ancestor. This technique is widely used, for example to establish that our common ancestor with chimpanzees lived at least 7 million years ago.
"RNA viruses such as HIV evolve approximately 1 million times faster than human DNA," says Faria. This means the HIV "molecular clock" ticks very fast indeed.
HIV originating from apes typically belongs to a type of virus called HIV-1. One is called HIV-1 group O, and human cases are largely confined to west Africa.
In fact, only one form of HIV has spread far and wide after jumping to humans. This version, which probably originated from chimpanzees, is called HIV-1 group M (for "major"). More than 90% of HIV infections belong in group M. Which raises an obvious question: what's so special about HIV-1 group M?
It is not especially infectious, as you might expect. Instead, it seems that this form of HIV simply took advantage of events. "Ecological rather than evolutionary factors drove its rapid spread," says Nuno Faria at the University of Oxford in the UK.
Faria and his colleagues built a family tree of HIV, by looking at a diverse array of HIV genomes collected from about 800 infected people from central Africa.
The very first person to be infected with HIV-1 group M probably picked up the virus in the 1920s
Genomes pick up new mutations at a fairly steady rate, so by comparing two genome sequences and counting the differences they could work out when the two last shared a common ancestor. This technique is widely used, for example to establish that our common ancestor with chimpanzees lived at least 7 million years ago.
"RNA viruses such as HIV evolve approximately 1 million times faster than human DNA," says Faria. This means the HIV "molecular clock" ticks very fast indeed.
понедельник, 07 июля 2014
Archaeopteryx had pennaceous (quill-like) feathers all over its body, not only its wings, a new fossil - only the 11th of the creature found - reveals.
These "trousers" were probably used for display, say scientists from Germany, writing in Nature journal.
Their discovery adds weight to the theory that feathers originally evolved for purposes other than flight.
Flight mystery
Continue reading the main story
“Start Quote
I'm pretty sure it could fly, though there is still a debate about how well it could fly”
Dr Oliver Rauhut, Bavarian State Collection for Palaeontology and Geology
reenex hong kong
Archaeopteryx caused a major stir when the first fossil was unearthed in Germany in 1861 - just two years after Charles Darwin published On The Origin of Species.
With the claws and teeth of a dinosaur, but the feathers of a bird, it was clearly a transitional form - apparent proof of Darwin's theory.
Its German name "Urvogel" means "first bird".
And though earlier bird-like dinosaurs have been unearthed since, many scientists still believe Archaeopteryx was the first capable of "flight" as we know it today.
The 11th fossil specimen was announced in 2011 and is remarkably well preserved, with detailed impressions of feathers all over its skeleton. The feathers are long and symmetrical on its upper leg and shorter lower down.reenex 效果
These "trousers" were probably used for display, say scientists from Germany, writing in Nature journal.
Their discovery adds weight to the theory that feathers originally evolved for purposes other than flight.
Flight mystery
Continue reading the main story
“Start Quote
I'm pretty sure it could fly, though there is still a debate about how well it could fly”
Dr Oliver Rauhut, Bavarian State Collection for Palaeontology and Geology
reenex hong kong
Archaeopteryx caused a major stir when the first fossil was unearthed in Germany in 1861 - just two years after Charles Darwin published On The Origin of Species.
With the claws and teeth of a dinosaur, but the feathers of a bird, it was clearly a transitional form - apparent proof of Darwin's theory.
Its German name "Urvogel" means "first bird".
And though earlier bird-like dinosaurs have been unearthed since, many scientists still believe Archaeopteryx was the first capable of "flight" as we know it today.
The 11th fossil specimen was announced in 2011 and is remarkably well preserved, with detailed impressions of feathers all over its skeleton. The feathers are long and symmetrical on its upper leg and shorter lower down.reenex 效果
вторник, 11 февраля 2014
GM had previously said Ms Barra would be paid $4.4m in cash and stock this year, but that figure did not include long-term
compensation.Maggie Beauty
The disclosure comes after the firm had been criticized by some for underpaying Ms Barra for her gender.
GM released the salary number "to correct misperceptions".
"As a new CEO, Mary's total compensation is in line with her peer group and properly weighted so that most is at-risk," said GM
board chairman Tim Solso in a statement.Invisalign
auty
"The company's performance will ultimately determine how much she is paid."
The compensation is subject to shareholder approval at GM's annual meeting in June.
Ms Barra took over the helm of the US's largest car firm on 15 January, after Mr Akerson stepped down to take care of his ailing
wife.
She is the first female boss of a major car manufacturer.iphone 3 cases
compensation.Maggie Beauty
The disclosure comes after the firm had been criticized by some for underpaying Ms Barra for her gender.
GM released the salary number "to correct misperceptions".
"As a new CEO, Mary's total compensation is in line with her peer group and properly weighted so that most is at-risk," said GM
board chairman Tim Solso in a statement.Invisalign
auty
"The company's performance will ultimately determine how much she is paid."
The compensation is subject to shareholder approval at GM's annual meeting in June.
Ms Barra took over the helm of the US's largest car firm on 15 January, after Mr Akerson stepped down to take care of his ailing
wife.
She is the first female boss of a major car manufacturer.iphone 3 cases