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Sidste sommer på Mars

This image was acquired at the Phoenix landing site on day 73 of the mission on the surface of Mars, or Sol 72, after the May 25, 2008, landing. The surface stereo imager left acquired this image at 10:29:32 local solar time. The camera pointing was elevation -42.7538 degrees and azimuth 57.3652 degrees.

This image was acquired at the Phoenix landing site on day 101 of the mission on the surface of Mars, or Sol 100, after the May 25, 2008, landing. The surface stereo imager left acquired this image at 16:04:58 local solar time. The camera pointing was elevation -47.6297 degrees and azimuth 64.1583 degrees.

This image was acquired at the Phoenix landing site on day 31 of the mission on the surface of Mars, or Sol 30, after the May 25, 2008, landing. The surface stereo imager right acquired this image at 16:16:24 local solar time. The camera pointing was elevation -27.2258 degrees and azimuth 281.163 degrees.

This image was acquired at the Phoenix landing site on day 31 of the mission on the surface of Mars, or Sol 30, after the May 25, 2008, landing. The surface stereo imager right acquired this image at 16:49:03 local solar time. The camera pointing was elevation -64.2742 degrees and azimuth 132.477 degrees.

The Y chromosome has sex with itself to guard against mutation.

Y chromosome sequence completed

DNA readout reveals genetic palindromes safeguard male-defining
chromosome.

Reports of the demise of the Y chromosome and an impending
extinction of men may have been exaggerated. The Y's full genome
sequence reveals that we have underestimated its powers of self-
preservation.

Instead of doubling up to protect its genetic cargo like other
chromosomes, the lone Y safeguards its genes by having sex with
itself, an international consortium has found.

"We're on a quest to bring respectability to the Y chromosome," says
geneticist David Page of the Massachusetts Institute of Technology,
leader of the sequencing team. The male-defining chromosome was
previously thought of as a wasteland where genes go to die.

The Y's defences are double-edged, however, sometimes leading to
infertility. The sequence should help us to diagnose and treat such
genetic mishaps.

Two-way street

Human chromosome pairs swap genes to minimize bad mutations. Y,
which has no partner, faces being whittled away by mutation. Some
estimate that the chromosome could be complete junk in about ten
million years.

The finished sequence shows that the chromosome fights entropy with
palindromes. About six million of its 50 million DNA letters reside in
sequences that read the same, in opposite directions, on both strands
of the double helix. The longest is nearly three million letters long1.
"The Y chromosome is a hall of mirrors," says Page.

These palindromes house many genes - which means that there is a
copy at each end of the palindromic sequence. These provide back-
ups should harmful mutations arise. The mirror-image structure also
allows the arms to swap position when DNA divides. Genes are
shuffled and bad copies are purged.

There are 50 million letters in Y's finished sequence.

Page's team has calculated the amount of swapping needed in each
generation to produce the near-perfect palindromes of the human Y.
They estimate that every man's Y contains 600 DNA letters that differ
from his father's2. This is thousands of times more than the normal
mutation rate.

"No one had contemplated that there would be this level of gene
conversion in our own genome," says Huntington Willard of Duke
University, Durham, North Carolina. "It gives us a glimpse of how the Y
has protected itself."

Other researchers see swapping as an evolutionary accident, not a
safeguard. "It's a daring suggestion, but I find it a bit difficult to
believe," says geneticist Mark Jobling of the University of Leicester,
UK.

Jobling is sceptical because the trick has a high cost: good genes are
just as liable to be lost as bad. This is a major cause of male infertility,
as most of the genes within the palindromes control testes
development. One in every few thousand men is infertile because key
genes have been deleted.

Y files

Genetic testing is already used to diagnose male infertility. A fuller
understanding of the Y's make-up will help refine these tests, and
improve doctors' advice to couples. "We have a greater knowledge of
where the Y tends to break," says Page. "Testing needs to be updated
to reflect our better understanding from the finished sequence."

The palindromes, and other forms of repeated DNA, made the Y
chromosome very tricky to sequence. So the finished sequence comes
from just one man's Y. Getting more sequences is essential, says
Jobling, as the chromosome's structure, and hence biology, varies
greatly around the world.

"We have a beautiful snapshot of the Y chromosome," he says. "Now
we need to look in other lineages to build up a photo album of its
diversity."

Source: Nature.com

OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR

Ford Wyoming Drive In

SPAMBOX

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mig >>Sandy gave your mail

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nagyslazlo >>We can help you.

bayramakcakaya >>Fall asleep, fall asleep

mig >>Everything's cancelled today

Jeremy >>Be kind to answer

mig >>Asked for me?

Yolanda >>Hello

rmmsail1 >>Well, what now?

maintman65 >>Fill full her box

Felkner Ovqu >>Contact me in 1 hour

—

HOW TO DETECT A 2-WAY MIRROR

Kort film her.

double

double
/ˈdʌbəl/
adj
consisting of two parts that are similar or exactly the same;
combining or involving two things of the same type;
twice as big, twice as much, or twice as many as usual;
made for two people or things to use;
used to say that a particular letter or number is repeated;
a double flower has more than the usual number of petals;