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Sex, cleaner of genomes
Indiana University via biologynews.net ^ | February 16, 2006 | NA

Posted on 06/22/2008 2:11:51 AM PDT by neverdem


The water flea Daphnia pulex is a commonly used model organism among ecologists and other environmental scientists.
Copyright Holder: P.D.N. Hebert, University of Guelph

When sexual species reproduce asexually, they accumulate bad mutations at an increased rate, report two Indiana University Bloomington evolutionary biologists in this week's Science. The researchers used the model species Daphnia pulex, or water flea, for their studies.

The finding supports a hypothesis that sex is an evolutionary housekeeper that adeptly reorders genes and efficiently removes deleterious gene mutations. The study also suggests sexual reproduction maintains its own existence by punishing, in a sense, individuals of a species that meander into asexuality.

"It is known that sex is common in plants and animals, and that asexual species are typically short-lived, but why this should hold throughout evolutionary time is a great mystery," said Susanne Paland, who led the study. "Our results show that asexual deviants are burdened by an ever-increasing number of genetic changes that negatively affect the function of their proteins. It appears sex is important because it rids genomes of harmful mutations."

Coauthor Michael Lynch added, "Although there has been solid theory on the matter for quite some time, these results provide the first definitive proof at the molecular level that sexual reproduction magnifies the efficiency of natural selection in eliminating deleterious mutations from populations."

Sexual reproduction is biologically costly and at times complicated. In mammals, sex is usually preceded by intricate mating behaviors. It requires the compatibility of sexual structures, an insertion event, fertile eggs and sperm, and the successful unification of egg and sperm into a viable zygote. All of this adds up to a big energy investment -- energy an organism might have used for other purposes. Scientists have long been left to ponder, what is it about sex that justifies its big energy investment?

Biologists have come up with a wide variety of competing (and, in some cases, complementary) hypotheses to explain why sex continues to exist in the midst of recurrently evolving asexual competitors. The most widely accepted explanation has been that sexual reproduction confers the benefit of "unlinking" genes, meaning bad versions of genes won't always get to ride the coattails of good versions, and vice versa. In essence, the theory holds that natural selection operates best when parts of the genome are free to shuffle.

The present report provides evidence this is so. In the case of Daphnia pulex, sex appears to have enabled the separation of beneficial and deleterious versions of genes, so natural selection could act more efficiently in favoring the good and weeding out the bad.

The scientists used mitochondrial genome data to compose a phylogenetic tree depicting relationships among sexual and asexual strains of Daphnia pulex sampled from 75 ponds as far west as Illinois and as far east as Nova Scotia, Canada. This family tree reveals that sexual populations have recently and repeatedly spun off asexual strains.

The scientists sequenced the entire mitochondrial genomes for a subset of these sexual and asexual lines of Daphnia pulex, and by comparing rates of protein evolution, they found the asexual lines have accumulated bad mutations four times faster than sexual lines.

Paland and Lynch reason that if a switch to asexuality causes a big increase in the number of protein defects, a mechanism for removing those defects must somehow be missing when sex, too, is missing. The present report supports the notion that it is sex -- or genetic recombination that is a component of sexual reproduction -- which is the purifying force that helps get rid of genetic mishaps that harm the overall evolutionary health of a population.

The ability to reproduce asexually may be useful to organisms that can't get mates, but its long-term benefits are questionable.

"Ultimately, we would like to know how long a species can abstain from sex without going extinct," Lynch said.

Source : Indiana University


TOPICS: Culture/Society; News/Current Events
KEYWORDS: genetics; genomes; genomics; godsgravesglyphs; sex

1 posted on 06/22/2008 2:11:51 AM PDT by neverdem
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To: neverdem
In mammals, sex is usually preceded by intricate mating behaviors.

Indeed.

2 posted on 06/22/2008 2:16:03 AM PDT by Jeff Chandler (Given such dismal choices, I guess I'll vote for the old guy.)
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To: neverdem
This family tree reveals that sexual populations have recently and repeatedly spun off asexual strains.

I would think that some environmental stress would cause the spin off of an asexual strain. Perhaps a die off of prey or a particularly cold year.

3 posted on 06/22/2008 2:39:18 AM PDT by Pontiac (Your message here.)
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To: neverdem
"Ultimately, we would like to know how long a species can abstain from sex without going extinct,"

Doh! :-O

4 posted on 06/22/2008 2:58:39 AM PDT by Diva
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To: neverdem
sex appears to have enabled the separation of beneficial and deleterious versions of genes

Is this where can I get me one of those sex licenses?

5 posted on 06/22/2008 3:03:37 AM PDT by ninonitti
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To: neverdem

“When sexual species reproduce asexually, they accumulate bad mutations at an increased rate”
Take note. CLONING is reproducing asexually, so CLONING will cause big trouble with abnormal mutations.


6 posted on 06/22/2008 3:42:51 AM PDT by BooksForTheRight.com (Fight liberal lies with knowledge. Read conservative books and articles.)
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To: neverdem

Guilty.

7 posted on 06/22/2008 4:17:56 AM PDT by the invisib1e hand (the media vs. the people.)
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To: neverdem
Sex ... is ... costly and at times complicated.

No kidding.

8 posted on 06/22/2008 4:49:34 AM PDT by Sherman Logan (Those who deny freedom to others deserve it not for themselves. - A. Lincoln)
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To: neverdem
"Scientists have long been left to ponder, what is it about sex that justifies its big energy investment?"

Doesn't have a clue, does he? And people wonder why scientists are considered to be nerds.

9 posted on 06/22/2008 4:54:24 AM PDT by norwaypinesavage (Planting trees to offset carbon emissions is like drinking water to offset rising ocean levels)
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To: neverdem
The scientists sequenced the entire mitochondrial genomes...and...found the asexual lines have accumulated bad mutations four times faster than sexual lines.

This is confusing. At least in humans, mitochondrial DNA is supposed to be asexually reproduced, coming only from the mother. Is that not the case with water fleas?

10 posted on 06/22/2008 5:37:05 AM PDT by hellbender
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To: neverdem
Sexual reproduction is biologically costly and at times complicated. In mammals, sex is usually preceded by intricate mating behaviors. It requires the compatibility of sexual structures, an insertion event,...

New recommended pick up line, "Want to take part in an insertion event?"

11 posted on 06/22/2008 5:38:03 AM PDT by SampleMan (We are a free and industrious people, socialist nannies do not become us.)
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To: norwaypinesavage
"Scientists have long been left to ponder, what is it about sex that justifies its big energy investment?"

Doesn't have a clue, does he? And people wonder why scientists are considered to be nerds.

Chantilly Lace had a pretty face and a ponytail hangin' down
A wiggle in her walk and a giggle in her talk
Make the world go 'round
Ain't nothing in the world like a big eyed girl
To make me act so funny, make me spend my money
Make me feel real loose like a long necked goose
Like a--oh baby, that's a-what I like!

12 posted on 06/22/2008 8:37:33 AM PDT by Ghengis (Of course freedom is free. If it wasn't, it would be called expensivedom. ~Cindy Sheehan 11/11/06)
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To: Sherman Logan

Don’t forget smelly.


13 posted on 06/22/2008 12:42:33 PM PDT by fieldmarshaldj (~"This is what happens when you find a stranger in the Alps !"~~)
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To: neverdem; martin_fierro

Thanks neverdem for both of these.

Chromosome rearrangements not as random as believed
Children’s Hospital of Philadelphia via biologynews.net | February 16, 2006 | NA
Posted on 06/22/2008 3:02:05 AM PDT by neverdem
http://www.freerepublic.com/focus/f-news/2034639/posts


14 posted on 06/22/2008 5:32:48 PM PDT by SunkenCiv (https://secure.freerepublic.com/donate/_________________________Profile updated Friday, May 30, 2008)
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To: blam; StayAt HomeMother; Ernest_at_the_Beach; 1ofmanyfree; 21twelve; 24Karet; 2ndDivisionVet; ...

· join list or digest · view topics · view or post blog · bookmark · post a topic ·

 
Gods
Graves
Glyphs
Thanks neverdem.

To all -- please ping me to other topics which are appropriate for the GGG list.
GGG managers are Blam, StayAt HomeMother, and Ernest_at_the_Beach
 

· Google · Archaeologica · ArchaeoBlog · Archaeology magazine · Biblical Archaeology Society ·
· Mirabilis · Texas AM Anthropology News · Yahoo Anthro & Archaeo ·
· History or Science & Nature Podcasts · Excerpt, or Link only? · cgk's list of ping lists ·


15 posted on 06/22/2008 5:34:18 PM PDT by SunkenCiv (https://secure.freerepublic.com/donate/_________________________Profile updated Friday, May 30, 2008)
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To: SunkenCiv
The researchers used the model species Daphnia pulex

Ah, good ol' Daphne Pulex.

Good times. Good times.

16 posted on 06/22/2008 5:48:18 PM PDT by martin_fierro (< |:)~)
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To: neverdem

Sex, cleaner of genes???

I know a gal whose jeans I’d like to...
ummm... do some bioengineering with.


17 posted on 06/22/2008 5:50:20 PM PDT by djf (I don't believe in perpetual motion. Perpetual mutton, that's another thing entirely!)
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To: martin_fierro

She was dating both of us at the time, though...


18 posted on 06/22/2008 6:35:25 PM PDT by SunkenCiv (https://secure.freerepublic.com/donate/_________________________Profile updated Friday, May 30, 2008)
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To: neverdem

Even ugly water fleas
Do it


19 posted on 06/23/2008 3:13:43 AM PDT by 668 - Neighbor of the Beast (Teach your child to be an American. Take him out of public school.)
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To: neverdem
The ability to reproduce asexually may be useful to organisms that can't get mates, but its long-term benefits are questionable.

If I sit here long enough, I'll double in size?

20 posted on 06/23/2008 3:16:46 AM PDT by 668 - Neighbor of the Beast (Teach your child to be an American. Take him out of public school.)
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To: neverdem
"Ultimately, we would like to know how long a species can abstain from sex without going extinct," Lynch said.

I wonder if we can volunteer the species of Liberalis Americanus for the above mentioned experiment...

21 posted on 06/23/2008 1:20:33 PM PDT by coconutt2000 (NO MORE PEACE FOR OIL!!! DOWN WITH TYRANTS, TERRORISTS, AND TIMIDCRATS!!!! (3-T's For World Peace))
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