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Old 15-11-2006, 21:42   #1
haku haku is offline
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Science articles

This is some pretty exciting news, we'll learn a great deal from the comparison between our genome and the Neanderthal genome.


Neanderthal genome sequenced within two years

Neanderthals have genome chunk sequenced

What are the genetic changes that set us apart from our Neanderthal cousins? Although the ancient race is long extinct, we may soon know the answers.

More than one million base pairs of fossilised Neanderthal DNA have now been sequenced – the most of any extinct organism – thanks to a new high-throughput sequencing technique well-suited to handling old, degraded DNA.

Two research teams collaborated closely on the project – the first steps towards sequencing the Neanderthal genome – in a marked difference to the competitive race to for the human genome.

Both teams used the same 38,000-year-old Neanderthal specimen, discovered in Croatia, from which to extract DNA and report their findings on Wednesday in the journals Nature and Science, respectively.

Common ancestor

The sequence suggests that humans and Neanderthals probably began to diverge about 600,000 years ago, and that our common ancestor lived in a small population comprising just 3000 individuals.

One group, led by palaeogeologist Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, used the rapid new "direct sequencing approach" on DNA culled from the ancient hominid’s thighbone. The technique was developed by research collaborators 45 Life Sciences, based in Branford, Connecticut, US.

The other team, led by geneticist Eddy Rubin at the Lawrence Berkeley National Laboratory, Walnut Creek, California, US, used a more traditional sequencing method involving cloning DNA using bacteria to generate 630,000 base pairs of the Neanderthal sequence.

Time difference

The studies only explored a tiny fraction of the full genome, and so the insights they provide are limited, so far. But both teams were able to use their results to estimate how long ago humans and Neanderthals shared a common ancestor.

Paabo’s group puts the date at around 516,000 years ago, while Rubin’s team reaches a slightly older date of 706,000 years ago. Both estimates have large errors of margin that in fact overlap, so the dates are broadly compatible.

One of the major problems confronting efforts to sequence such ancient DNA is contamination, both from microbial DNA and, more significantly, from modern human DNA, which could be confused with Neanderthal sequences. Researchers in both teams used a number of tests to ensure that they were working with genuine Neanderthal DNA, however.

“This is proof of principle that we can recover nuclear genome sequences from Neanderthals,” says Richard Green, one of Paabo’s team. We should have the full genome sequenced within two years," he says.

New Scientist
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Last edited by haku; 30-03-2007 at 18:27.
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Old 30-03-2007, 18:24   #2
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Planets are common around tight stellar pairs

The Star Wars scene in which Luke Skywalker stares out at two sunsets may not be so outlandish, according to new observations by the Spitzer Space Telescope.

In fact, the research suggests that planets in double-star systems are at least as common as those around single stars – and are even more common around stars that orbit each other closely, like the system depicted in Star Wars. This could give astronomers a whole new avenue for searching for planets, and possibly even life.

Astronomers know that planets can form around double stars. Some form around just one of the stars in the pair if the two stars are far away from each other, lying at least 1000 astronomical units apart (1 AU is the distance between the Sun and the Earth). About 50 of the 200 known planets outside our solar system orbit one of the stars in a widely separated binary pair (see The riddle of the inflatable planets).

But it was not clear how common planets were around stars that orbited each other more tightly (although one such system, involving a trio of stars, was discovered in 2005).

Now, astronomers led by David Trilling of the University of Arizona in Tucson, US, have completed the most comprehensive survey ever done on binary systems in which the stars are relatively close to one another – lying between 0 and 500 AU apart.

Dusty discs

They looked at 69 such systems between 50 and 200 light years from Earth, searching for evidence that one or both stars were surrounded by dusty discs. The dust in these discs could have been produced by collisions between asteroids, suggesting planets might also have formed in the discs.

About 60% of the binary star systems that were closest together – no more than 3 AU apart – had dusty discs surrounding the pair. In comparison, only about 20% of the single stars in a similar sample had dusty discs. Watch an animation of a planetary system around a tight stellar pair (3 MB, Windows Media format).

"We found that it appears that planetary system formation is at least as common in binary star systems as it is in single star systems," Trilling told New Scientist. "That's important because two-thirds of the [bright] stars in our galaxy are in binary or multiple star systems. That says that the number of potential sites for planets in the galaxy just went up enormously."

Kick start

The reason why planets are so common around these snug binary systems could be that the second star's gravity could help stir up the discs of gas and dust from which planets form, kick-starting their growth, says Trilling.

However, dusty discs were not common around binary stars lying an intermediate distance – from 3 to 50 AU – apart. Trilling says that may be because there are gravitational instabilities around such systems that eject planets and dust. Alternatively, the systems may boast dusty discs that are simply too far away from the stars – and thus too cold – for Spitzer to detect.

For stars farther apart than 50 astronomical units, planets could just orbit one of the stars, instead of both, he says.

Although the existence of dusty discs is often taken as a sign of possible planet formation, Trilling says it is possible that there are no planets in these discs. That is because the two stars may have created a lot of gravitational turbulence that prohibited the asteroid-sized bodies from ever forming planets.

The possibility of life is not yet ruled out for multiple star systems, like in Star Wars. "There's nothing I can see that is astronomically wrong with their science fiction," Trilling says.

New Scientist
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Old 13-04-2007, 15:47   #3
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The rhesus macaque has become the third primate to have its genome fully sequenced, joining humans and chimpanzees.

The newly completed genome gives biologists a much deeper understanding of a crucial organism in biomedical research. It also offers evolutionary biologists a vantage point from which they can better understand the genetic changes that turned humans into such unusual apes.

An international consortium [http://www.hgsc.bcm.tmc.edu/projects/rmacaque/] of more than 170 scientists at 35 institutions sequenced the entire genome of a female macaque living at a research centre in San Antonio, Texas, US.

The macaque's nearly 3 billion DNA base pairs are 93.5% identical to those found in the human genome, as expected for a species whose lineage diverged from that of humans about 25 million years ago. By comparison, the human and chimp genomes, which diverged about six million years ago, are about 98% identical.

The rhesus macaque is already a valuable study organism for biomedical research, including drug testing and work on infectious diseases such as HIV and influenza. With genome in hand, biologists should now be able to refine their experiments by focusing on animals bearing particular genetic traits, thus gleaning more information from fewer animals, says Richard Gibbs, a geneticist at Baylor College of Medicine in Houston, Texas, who led the macaque sequencing consortium.

Resolving uncertainty

Having three genomes from closely related primate species also gives biologists much greater leverage in understanding primate evolution. Before, if the human and chimp versions of a gene differed, there was no way to know which of the two had been modified from the ancestral version.

Now, biologists can look to the macaque version to resolve the uncertainty. "We can take an unbiased look at what the genome is telling us needed to change," says David Haussler at the University of California at Santa Cruz in the US.

A genome-wide search turned up over 200 genes that appear to have evolved under natural selection in either the macaque or human-chimp lineages since the two diverged. Since these genes represent the levers by which evolution led humans to differ from macaques, researchers will be looking closely at them to help understand the evolution of modern humans.

Thinking caps

The gene list identified so far includes genes for hair structure, immune response, intercellular communication and sperm-egg fusion – but not, apparently, for brain size.

One puzzling discovery is that several mutations that cause genetic diseases in humans – such as phenylketonuria and Sanfillipo syndrome, which lead to mental retardation – are in fact the normal form found in macaques and, presumably, our own distant ancestors. "How can genes that seem to be fine in one species give disease in another closely related one?" asks Gibbs.

Such delicately balanced genes may be a good place to look for some of the key steps in the evolution of modern humans. Some cases of mental retardation, he speculates, may even result from mutations that return a key gene to its ancestral condition.

New Scientist
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Old 02-05-2007, 00:14   #4
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Female ducks fight back against raping males

Some female ducks and geese have evolved complex genitalia to thwart unwelcome mating attempts, according to a new study.

Males of some species, such as mallard, have a notorious habit of "raping" females. They and other wildfowl are among the 3% of bird species whose males have phalluses big enough to insert into the vaginas of females, whether or not the female consents.

Now, in the most detailed analysis yet of duck and goose vaginas, researchers have established that females of these species have evolved vaginal features to thwart unwelcome males.

Tim Birkhead at the University of Sheffield in the UK and colleagues examined vaginas and the corresponding phalluses from 16 wildfowl species. They discovered that the longer and more elaborate the male member, the longer and more elaborate its female recipient was.

No-entry signs

Some vaginas had spiral channels that would impede sex by twisting in the opposite direction to that of the male phallus. Others had as many as eight cul-de-sac pouches en route, that could prevent fertilisation by capturing unwelcome sperm. Moreover, these features were only found in species renowned for forced sex. All other species had simple male and female genitalia.

“These structures are wonderfully devious, sending sperm down the wrong road or impeding penetration,” says Birkhead.

He says that the features demonstrate an evolutionary "arms race" in which control over reproduction alternates between the sexes. If the male develops a longer, more elaborate phallus to force copulation, females wrest back control by developing features to thwart males who rape.

“It shows that females are not passive in averting exploitation by males with large phalluses,” says Birkhead.

New Scientist
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Old 02-05-2007, 09:05   #5
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Okay that's really interesting. Evolution always amazes me. I just didn't know it works in such short time-spans as well. I thought it usually takes thousands of years for any noteworthy changes.

In any case... I just wonder how some people even came up with the IDEA of doing the study. Were they just sitting in the office one day going: "Hey I've got an idea...lets conduct the most detailed analysis YET of duck and goose vaginas!" Others: "Brilliant!"
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Religion is an insult to human dignity. With or without it you would have good people doing good things and evil people doing evil things. But for good people to do evil things, that takes religion.
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