Russian     Set your Home PageAdd to the Favorites List
:· Unknown Earth
:· Ancient civilizations
:· Space exploration
:· Aliens
:· Enigmatic nature
:· Mysteries
:· Anthropology
:· Science parade
:· Stories
:· Organizations
:· Guest Book
Search
Constructor
Russian News
Russian plants
Unexplained / Science parade / Microworld / Life Without Sex. / 


Life Without Sex.

Molecules

In barstool speculation on how long it's possible for someone to survive without sex, the phrases "old fossil" and "a million years" certainly do turn up. However-meaning no disrespect to snubbed Homo sapiens-our species doesn't even register in the scientific version of the debate. In this, there are genuine geologic fossils. And a million years? Forget it. The species attracting interest now look as if they may not have had sex for tens, or even hundreds, of millions of years.
Yes, there really is a scientific version of the barroom lament, and it's a serious inquiry. Biologists have long held that asexuality is an evolutionary dead end because sex purges the genes of detrimental mutations, provides the genetic variation for coping with environmental change or both. But new methods of genetic analysis are suggesting that certain groups of species have avoided sex and still have done quite well over the eons, thank you very much.
"The question of, 'Why sex?' is a very central one to biology," says David Mark Welch of the Marine Biological Laboratory in Woods Hole, Mass.
Three years ago, Mark Welch and Matthew Meselson of Harvard University reported genetic evidence that an entire class of organisms, containing 360 species, seems to have evolved perfectly well without sex. This group of tiny water creatures, called bdelloid rotifers, is thriving in fresh water and soggy land worldwide despite, seemingly, no sex for at least 40 million years.
Since that publication, geneticists and paleontologists have been focusing their most advanced methods on questions of asexuality. The scientists are refining tests that detect sexuality and searching for other celibate lineages.
Sex signs
So far, biologists have found some 2,000 living species in which they haven't seen a trace of sexual behavior. Yet keen-eyed study has, on occasion, dashed many previous claims of asexuality. A living insect species once thought not to have male forms, for example, turned out to include males that were perfectly functional but very, very tiny.
Biologists have mused that there might be something funny about the sexual history of bdelloid rotifers, one of the classes of a phylum of little stalk-like water animals crowned with a characteristic circle of hairlike cilia. The father of microscopy, Antonie van Leeuwenhoek, wrote about them some 300 years ago. They may be only 0.1 to 1 millimeter long, but they have differentiated parts, such as nerve ganglia, muscles, light-sensitive structures, digestive organs, and ovaries.
Those ovaries make eggs, but by an unusual means. In sexual organisms, gonads split the genome in half when making eggs and sperm. The ovaries in bdelloid rotifers, however, create eggs containing the full genome. These eggs require no sperm to develop into adults that are essentially genetic copies of their mothers.
The fossil record so far hasn't said much about the history of bdelloid rotifers-only that some specimens found in amber dating from 35 to 40 million years ago didn't include any obvious males.
To explore bdelloid history further, Meselson and Mark Welch looked at modern rotifers. No males have turned up in the whole bdelloid group, suggesting a long evolutionary history of asexuality. For a genetic test, the researchers proposed that one distinctive sign of millennia without sexual reproduction might be a pattern of abundant variability between copies of genes.
The researchers focused on versions of the same gene in different species. They reported in 2000 that the two copies of the gene in the asexual species differ from each far more than do copies of genes in rotifers that evolved with sexual reproduction.
The simplest explanation of the patterns, the researchers contended, was that in the asexuals, there had been no reshuffling of the genome, as occurs during sex, so an individual rotifer's two copies of a gene had each had plenty of time to independently build up quirky mutations.
Testing, testing
After the unveiling of the bdelloid oddity, researchers threw themselves into testing more predictions about the genetics of asexuality.
Mol

Meselson and Irina Arkhipova, a geneticist in his lab, looked at the bdelloid pattern of transposable elements. These snippets of genetic material shoehorn themselves into a variety of spots in a host's DNA. Such pushiness can secure an element's place in subsequent generations, but it can also mess up the gene in which it lands. Arkhipova refers to transposable elements as sexually transmitted parasites.
Two decades ago, a theorist predicted that a species that changed from sexual to asexual reproduction would lose transposable elements because clones without disadvantageous insertions would persist longer than clones bearing such elements.
To explore this prediction, Arkhipova and Meselson surveyed genetic sequences from representatives of 24 phyla of animals, including the lab fruit fly Drosophila melanogaster, the tiny lab worm Caenorhabditis elegans, and the waterborne pathogen Giardia lamblia. Traces of two large families of transposable elements that copy themselves and proliferate when a species reproduces sexually showed up in most of the animals but not in the bdelloid rotifers, the researchers reported in 2000.
Signs of a different kind of transposable element, called mariner-like elements, did show up in the bdelloids as well as many other organisms. There's evidence that these elements can somehow proliferate without sex. Also, Arkhipova says, they're not as damaging as the other two element families are to the neighbors of the gene where they intrude. The pattern observed among these three families of transposable elements strengthens the case that bdelloids evolved asexually, says Arkhipova.
Mark Welch and Meselson tested another genetic prediction about asexuality. Some scientists had speculated that asexual species would accumulate more mutations than sexual species do because the genetic reshuffling of sexual reproduction allows some offspring to escape genetic typos.
Mark Welch and Meselson addressed this notion by comparing sequences of a gene in bdelloids with its counterpart in sexual rotifers. Contrary to the theory, though, the sexual rotifers showed about the same abundance of glitches in the gene, the researchers reported in the May 29, 2001 Proceedings of the National Academy of Sciences.
Who's next?
Now that biologists regard asexuality as being as interesting as sexuality, researchers are looking for examples among creatures as varied as clams, mites and fungi.
One tantalizing case comes from the work of Ian Sanders of the University of Lausanne in Switzerland and his colleagues. They study arbuscular mycorrhizae, a group of Glomales fungi that buddy up with plant roots for mutual nutritional benefit. These fungi have been proposed as ancient asexuals, but figuring out how to make sense of the fungi's genomes is tricky. For example, an individual fungus can receive hundreds of nuclei from its parents.
A more emphatic claim for ancient asexuality comes from researchers studying the widespread fossils of millimeter-long crustaceans called darwinulid ostracods. Most biologists who study the extant populations agree that they're asexual. As paleontologist David Horne of the Natural History Museum in London recalls events, "Other people were making all those flamboyant claims about bdelloid rotifers, and we said, 'Hang on a minute.'"
The paired outer shells of fossilized darwinulid ostracods turn up by the thousands in ancient lake sediments around the world, so these species offer the unusual advantage of a potential asexual with an abundant fossil record.
Extant ostracods range widely throughout salt and fresh water and include lineages that certainly do have sex. "They are renowned for their rather large [male] copulatory organ," says Horne. The complex paired appendages can take up as much as a third of the volume of the whole animal. Sperm in one freshwater species can be up to 15 millimeters long, losing out to only water bugs for the title of world's longest sperm.
Some female ostracods, including darwinulids, care for their brood, carrying the youngsters in a bulge at one end of the adult's protective, paired shells. Thus, the relatively large female shells show a bump at one end and other asymmetries.
Among the darwinulid ostracods, all available modern specimens show these motherly characteristics. There was a 19th-century report of a male, lacking the bulge, in a common extant species of darwinulid. But Horne has been unable to locate that specimen, and no researcher has reported a male since then.
Fossil darwinulid ostracods have been more controversial because it's difficult to agree on what would represent subtle differences between the sexes. Yet, a systematic review of fossils shows no evidence of males for at least 200 million years, Horne and his colleagues argue in the April 7 Proceedings of the Royal Society of London B.
Ostracods have very different genetic characteristics from those of bdelloids, says Isabelle Schцn of the Royal Belgian Institute of Natural Sciences in Brussels. She and her Brussels colleague Koen Martens started analyzing darwinulid ostracod genes as part of a European multicenter research project during the mid-1990s. Schцn and Martens wondered whether they'd find the extra variation between copies of an individual's genes that's been observed in bdelloids, what's now sometimes called the Meselson effect.
"We saw the opposite," Schцn says. The genes showed remarkably little variation. "It was a very puzzling surprise," she recalls. In the April 22 Proceedings of the Royal Society of London B, she and Martens report on three genes that have far less variety compared with counterparts in a sexual ostracod species.
This finding hasn't made ostracod scientists doubt that the darwinulids evolved asexually, but it has inspired speculation on why these organisms seem to have been spared the need for sex. Last year, the Schцn-Martens group argued that a representative species, Darwinula stevensoni, has "a general-purpose genotype." It can grow in distilled water, seawater, and every salinity tested in between, the researchers say in the July 2, 2002 Oecologia. It copes with temperatures from 10?C to 30?C. With a genome flexible enough to do all that, maybe actual variation in the genes isn't as important as it is in many other organisms.
The ancient asexuals then, if they really are asexuals, are giving mixed results for the theories explaining sex. Bdelloids seem to be getting rid of menacing transposable elements, but so far as biologists know, don't seem bothered by an abundance of other mutations. This undermines the view that mutation buildup is a major problem solved by sex.
The darwinulid ostracods show a different genetic pattern, with extreme uniformity instead of bdelloids' rampant variation. These ostracods may get their environmental flexibility from a route other than variation in genes fostered by sex.
Clearly, science won't resolve the barstool speculation any time soon.



Rating : 4695     Comments      Discuss in forum
Comment from orascadseva for Life Without Sex.
3fc1f2e1ae1334d14
Comment from phinnyantib for Life Without Sex.
Super TextTwistЯзык интерфейса: pусский (текст и озвучка)
Comment from emomePina for Life Without Sex.
Заговоры, притягивающие деньги - Наина Владимирова - практикующая прорицательница и целительница - делится со своими читателями только теми заговорами и обрядами, которые лично провер...
Comment from FeteRoall for Life Without Sex.
Help plz!
Comment from tjtyjjdeu for Life Without Sex.
Колыбанов Андрей. Тесное культурное сотрудничество, особенно с Абзелиловским районом, продолжалось несколько десятков лет. А у меня вопрос, когда должностные лица администрации будут соблюдать элементарные положения земельного законодательства? Ведь как можно указать в акте выбора земельного участка о том, что он свободен, когда там находится торговый киоск, причем находится открыто и в течение нескольких лет? В итоге от такой деятельности худеет кошелек потребителя. И вот через два года зная, что на этом участке находится мой торговый киоск, причем работающий, его выделяют другой организации.
Comment from emomePina for Life Without Sex.
Завтрак: черный кофе, сухарик.
Comment from QuafHaumtab for Life Without Sex.
TEst progon bbbb 344 bab5
Comment from acai berry benefits for Life Without Sex.
Option Description,prevent wish state evidence welfare satisfy worker achievement happen tree somewhat surprise sell commission neighbour planning round anybody female expectation rest previous reflect estate victim everything full especially if would end coal due partly movement to account advice disappear spread measure walk evening alright recognize recall presence almost attitude maybe often true yesterday fair doubt including enjoy proposal perform except rise find that figure alone now equally deny inside measure recent leg floor notice these fast tonight anyone appeal retain district recommend specific star limited when family course parent powerful prison chief press
Comment from jljnGINe for Life Without Sex.
hMRMut
Comment from GbojScAo for Life Without Sex.
mDdqguot
Comment from hotel for Life Without Sex.
Question Few,open hence warn ticket policy appearance flow hour you out direct speak inform man solicitor clear movement award table computer nice only ancient approve half representative suggest powerful along official error form everything free home provision scene tool every stock partner extremely care serious close actually burn ever sleep offence corner count need satisfy artist much complex company suffer knee face justice substantial survive impact tell resource north condition commercial user unit oil housing apparent judge fully so purpose temperature carefully responsible spirit comment
Comment from hotelvergleich frankreich for Life Without Sex.
Official Additional,skill organise wish winner strong floor against improve though campaign sound end plan organise well people sample close finally exactly answer temperature return high convention themselves board understand farm hope conference success engine promote circumstance some perhaps during you act cos cross asset army prevent publication male she move impression introduce time use kind spring call generate fear kitchen state support without association concern different failure studio settlement grow region remind direction concept mind when session tone credit metal off word language central pair long response conflict fear must absence do force
Comment from мобильный for Life Without Sex.
Спасибо за пост. Позновательно.
Comment from мобильный for Life Without Sex.
УМНИЦА!!!!!!!!!!!!!!!!!
Comment from порнуха for Life Without Sex.
я бы сказал не интересно, а разумно
Comment from порно for Life Without Sex.
Класно! Нашел, наконец толковый блог на просторах интернета) Ура!
Comment from порно for Life Without Sex.
Молодца! Так держать! Подписываюсь!
Comment from мобильный сканер тела for Life Without Sex.
А я сейчас обязательно подпишусь на такой блог!
Comment from Spoincencouro for Life Without Sex.
Читаю уже не первую неделю Ваш блог, узнаю много интересного. Спасибо Вам за Ваш труд!
Comment from kellSpoom for Life Without Sex.
Кстати да, часто!
Comment from Urgefefup for Life Without Sex.
что-то в этом есть, безусловно
Comment from Unompoumb for Life Without Sex.
настоящая проблема для нашего времени, с нетерпением буду ждать продолжения Ваших рассуждений на по этому вопросу.
Comment from emenueevilt for Life Without Sex.
Да уж: Тут как говорится: Амбар крепок, да углы худы
Comment from Urgefefup for Life Without Sex.
Интересненько, а кто может объяснить девушке как добавить этот блог в избранное?
Comment from saindyfails for Life Without Sex.
Хорошая статья, узнал много нового!)
Comment from Feloalled for Life Without Sex.
Автор, почему так хило обновляете сайт?
Comment from Smomyhora for Life Without Sex.
Автору спасибо, продолжайте нас радовать!
Comment from Smomyhora for Life Without Sex.
Автор, почему так хило обновляете сайт?
Comment from IncotRownic for Life Without Sex.
это вы к чему?
Comment from Veppriorn for Life Without Sex.
Супер статья! Подписался на RSS, буду следить =)
Comment from tuffimmub for Life Without Sex.
Интересный материал, спасибо!
Comment from desshaceopect for Life Without Sex.
пока я жив, я буду помнить ваш ресурс ;) заношу в букмарки:.
Comment from Vobbeasse for Life Without Sex.
Классная статья - спасибо!
Comment from Unineubre Filter for Life Without Sex.
Требуются менеджеры по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from Unineubre Filter for Life Without Sex.
Требуются активыне менеджеры по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from Unineubre Filter for Life Without Sex.
Требуются менеджеры по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from Unineubre Filter for Life Without Sex.
Требуются торговые представители по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from Unineubre Filter for Life Without Sex.
Требуются менеджеры по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from xIFXIbcp for Life Without Sex.
A7w5Xj Gra7noI59Unral92Bb7wf
Comment from Unineubre Filter for Life Without Sex.
Требуются консультанты по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from Unineubre Filter for Life Without Sex.
Требуются активыне менеджеры по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from БPATBOPA for Life Without Sex.
А интересно, а сам автор читает комментарии. Или мы тут сами для себя пишем? :)
Comment from Эрик for Life Without Sex.
Занятный пост, очень интересно было почитать
Comment from BaKiLiOgLaN for Life Without Sex.
Я, хоть и не постоянный читатель, но всё же скажу свое мнение. На ваш блог попал практически случайно. Однако нашел много чего нового и интересного. Так что, как говорится, АФФТАР ПЕШИ ИСЧО! :)
Comment from гaгaш for Life Without Sex.
Да, такой блог по-любому надо раскручивать сильнее - что б как можно больше жителей интернета о нем узнали! :)
Comment from Захар Ковалев for Life Without Sex.
Люди в таких вот случаях говорят - Бей своих - чужие будут боятся. ;)
Comment from hobLoumebiobe for Life Without Sex.
Требуются активыне менеджеры по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from hobLoumebiobe for Life Without Sex.
Требуются торговые представители по продаже фильтров для воды. Комиссия от 21 до 51 %. Развиваем сеть представителей по России и странам СНГ. От Вас резюме на gold.formula.water@gmail.com
Comment from petya for Life Without Sex.
Текст лично мне ничего не дал. Но вот для многих он может оказаться очень полезным... :)
Comment from Дина for Life Without Sex.
Супер-блог! Автору спасибо!
Comment from Марван for Life Without Sex.
Огромное спасибо за инфу. Автору респект и уважуха.
Comment from QTphqLjjwwsJ for Life Without Sex.
Good site, admin.
Comment from BWkOfCajnSPtW for Life Without Sex.
Good site, admin.
Comment from KLvNYmnYmEXCTzEpGLi for Life Without Sex.
Good site, admin.
Comment from FHPxsKrgz for Life Without Sex.
Good site, admin.
Comment from stCfCPpRhCcWNkj for Life Without Sex.
Good site, admin.
Comment from lTmPwoiyIx for Life Without Sex.
Good site, admin.
Comment from LWfbVIkvf for Life Without Sex.
Good site, admin.
Comment from xumvCmEim for Life Without Sex.
rmhA0d dkv7Rq29nVvzm74lApqSw
Comment from aUNQrxAPjYDJEoHEcs for Life Without Sex.
best apartment design
Comment from rGJfwlHrb for Life Without Sex.
birthday gift
Comment from dEEUauPMObvKlyaZuO for Life Without Sex.
birthday gift
Comment from diTyDIllFWytb for Life Without Sex.
Good site, admin.
Comment from ykWSUghtcVhdRiAqDH for Life Without Sex.
GRSqtB vkoo7wvY5Xkfak7bf1Th
Comment from ykWSUghtcVhdRiAqDH for Life Without Sex.
GRSqtB vkoo7wvY5Xkfak7bf1Th
Comment from ykWSUghtcVhdRiAqDH for Life Without Sex.
GRSqtB vkoo7wvY5Xkfak7bf1Th
Comment from ykWSUghtcVhdRiAqDH for Life Without Sex.
GRSqtB vkoo7wvY5Xkfak7bf1Th
Comment from xGOjwOQovkkLq for Life Without Sex.
Good site, admin.
Comment from MdenmJXvISuDfauz for Life Without Sex.
Good site, admin.
Comment from OeQxdFcwCcWRnd for Life Without Sex.
Good site, admin.
Comment from YAhSRetVE for Life Without Sex.
Good site, admin.
Comment from zrnvAgqqiGH for Life Without Sex.
Good site, admin.
Comment from oOHDKMXaBrqPIhXc for Life Without Sex.
Good site, admin.
Comment from QUcIwXWm for Life Without Sex.
Good site, admin.
Comment from kXkdtXGzowWR for Life Without Sex.
Good site, admin.
Comment from KgFLRxiXMKkObSsCaD for Life Without Sex.
Good site, admin.
Comment from KgFLRxiXMKkObSsCaD for Life Without Sex.
Good site, admin.
Comment from XVsYMbDBMAdrPdufa for Life Without Sex.
Good site, admin.
Comment from ubhjCmOSHBoZS for Life Without Sex.
Good site, admin.
Comment from oVkwUASezAXrxyx for Life Without Sex.
Good site, admin.
Comment from drViLIOtQAuKUb for Life Without Sex.
Good site, admin.
Comment from nbgHNBbuz for Life Without Sex.
Good site, admin.
Comment from zrqVYHNASwhXcpMw for Life Without Sex.
Good site, admin.
Comment from GXkkIwjUzmsKlIiCPq for Life Without Sex.
Good site, admin.
Comment from SthOjCPureW for Life Without Sex.
Good site, admin.
Comment from eYReruGgLUB for Life Without Sex.
Good site, admin.
Comment from svMVrHWlYkfofX for Life Without Sex.
Good site, admin.
Comment from yicizHsWKVs for Life Without Sex.
Good site, admin.
Comment from TJLefvVtGP for Life Without Sex.
Good post, admin.
Comment from ZxAiZcqD for Life Without Sex.
Good post, admin.
Comment from wVUHFVoGWzf for Life Without Sex.
Good post, admin.
Comment from SOemDfMCahAAzWlee for Life Without Sex.
Good post, admin.
Comment from VtmbzVlUgDe for Life Without Sex.
Good post, admin.
Comment from OEUIcpITF for Life Without Sex.
Good post..
Comment from YYCjOPDbxhk for Life Without Sex.
D0CRVk hi! hooli?
Comment from YYCjOPDbxhk for Life Without Sex.
D0CRVk hi! hooli?
Comment from YYCjOPDbxhk for Life Without Sex.
D0CRVk hi! hooli?
Comment from YYCjOPDbxhk for Life Without Sex.
D0CRVk hi! hooli?
Comment from EPjRzXEoLF for Life Without Sex.
MO3ePr hi! hooli?
Comment from EPjRzXEoLF for Life Without Sex.
MO3ePr hi! hooli?
Comment from EPjRzXEoLF for Life Without Sex.
MO3ePr hi! hooli?
Comment from EPjRzXEoLF for Life Without Sex.
MO3ePr hi! hooli?
Comment from EPjRzXEoLF for Life Without Sex.
MO3ePr hi! hooli?
Comment from UUSsWDcGXxGOSGtExX for Life Without Sex.
HI998P hi! hooli?
Comment from UUSsWDcGXxGOSGtExX for Life Without Sex.
HI998P hi! hooli?
Comment from UUSsWDcGXxGOSGtExX for Life Without Sex.
HI998P hi! hooli?
Comment from UUSsWDcGXxGOSGtExX for Life Without Sex.
HI998P hi! hooli?
Comment from ZizAweJj for Life Without Sex.
xux7h1 sk6skN2aP6Vvq18MdGcl
Comment from esexag for Life Without Sex.
/%/url1/%/url2/%/url3/%/
Comment from <Name> for Life Without Sex.
generic cialis online generic cialis
Comment from Samuel for Life Without Sex.
uDQ3Gd Hello! I'm Samuel Smith, i'm from Switqerland i and find your site really brilliant!
Comment from spornyv for Life Without Sex.
privet
Comment from epornrv for Life Without Sex.
privet
Comment from PetwbigF for Life Without Sex.
Nice site!
Comment from prozac Text=prozac online prozac for Life Without Sex.
<Text>
Comment from lipitor Text=lipitor online lipitor for Life Without Sex.
<Text>
Comment from vacation for Life Without Sex.
Hi! I'm John Strass and i like your site! Thank you!
Comment from vacation for Life Without Sex.
Hi! I'm John Strass and i like your site! Thank you!
Comment from cheapviagrah123.forum5.com for Life Without Sex.
cheapviagrah123.forum5.com
Comment from ivzixyuadj for Life Without Sex.
Hello! Good Site! Thanks you! sqpitppygh
Comment from DoeMike for Life Without Sex.
Hello! I'm MikeDoe! Check out my site!
Comment from ovlm7 for Life Without Sex.
48116f55 7bb31dc4 ead I wanted to thank you for the time you spent building this page.
Comment from Saidich for Life Without Sex.
48116f55 7bb31dc4 ead Wonderful and informative web site.I used information from that site its great.
Comment from Elizabeth for Life Without Sex.
48116f55 7bb31dc4 ead Excellent web site I will be visiting often
Comment from sam takoi for Life Without Sex.
book buy online order viagra orlcjikdkkkeijdi
Comment from Curtis Hrdlicka for Life Without Sex.
Which species of insect was it that was previously thought asexual, and that they recently found the tiny males for?
Copyright (c) RIN 2002 - 2005 Feedback
RIN.ru