Was watching House tonight ant there was a case that House was seeing in the Clinic and it was about
parthenogenesis [
virgin birth,
asexual reproduction] which occurs in rarely nature to [ex. bees, reptiles fish and even in some plants], but more rarely in humans which always results in a female child due to the XX chromosome. But a
hermaphroditic species can have both female and male off-springs as they have both XY chromosomes . Which can also, happen 1 in 5 million. The
discovery.com has information reptiles and other species... Very cool... Found some articles:
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Second 'Virgin Birth' Documented in Shark. Jennifer Viegas, Discovery News [10-10-08] (video:
A Mom Who Can Be Dad Too):
Oct. 10, 2008 --
The first documented virgin shark birth seemed like an odd miracle, but now a second female has become pregnant sans daddy, adding to the evidence that female sharks don't always need a male to conceive, according to a new study.
Virgin birth, scientifically known as
parthenogenesis, has previously been proven in certain amphibians,
reptiles, birds and bony fish. It's now suspected that most, if not all, female sharks possess the ability.
"Parthenogenesis may not have evolved in sharks," Demian Chapman, who led the research, told Discovery News. "It may just be an occasional mistake that sometimes occurs when eggs are left unfertilized."
Chapman, a shark scientist with the Institute for Ocean Conservation Science at Stony Brook University, explained that during egg production, a female shark produces four cells. Only one of these becomes the egg. Another of the four is called "the sister polar body," which is a close genetic match to the egg.
During parthenogenesis, according to Chapman, "the sister polar body fuses with the egg and injects its chromosomes into it."
Related Content:
Jennifer Viegas' blog: Born AnimalFemale Sharks Reproduce Without DadHow Stuff Works: Sharks"Therefore, it acts like a sperm and triggers the development of an embryo," he said.
The discovery in this case is bittersweet, since the virgin shark in question, a female blacktip shark named "Tidbit," died after living for eight years without a male companion at the Virginia Aquarium.
An autopsy upon her death revealed that she was pregnant with a single offspring. DNA testing of the unborn offspring showed that it contained no genetic material from a father.
A paper outlining the findings appears in the latest issue of the Journal of Fish Biology.
Chapman and his team made a similar discovery just last May, when a hammerhead residing at an Omaha, Neb., zoo became pregnant after not being in contact with male sharks for at least three years. DNA fingerprinting techniques were used in that case as they were for Tidbit.
The method is identical to how researchers handle human paternity testing.
Female sharks can store sperm for long periods of time, which is why the scientists needed to confirm, through the DNA analysis, the lack of paternal input.
Despite the novelty of the phenomenon, virgin births are inferior to regular shark births in two major respects.
First, the female appears to only be able to produce a single offspring in this manner. Females that mate can have litters ranging from a few to more than 100 shark pups, depending on the species.
Second, the offspring of a virgin birth has "reduced genetic diversity when compared to its mother or any other shark produced by sex," Chapman said, adding that the process is "no great white hope for depleted shark populations."
He hopes that future conservation efforts will focus on "robust shark populations with balanced gender ratios, rather than hoping for a bailout from some interesting quirk of reproduction."
Robert Hueter, director of the
Center for Shark Research at the Mote Marine Laboratory in Florida, told Discovery News that he supports the new findings since "the research methods are sound and the conclusion of a parthenogenetic birth in this shark species is proven."
Hueter said it's still possible that virgin births are more of "an egg developmental aberration rather than a physiological response to a lack of a mate," but he predicts "time will tell as more research is focused on this interesting subject."
Such revelations may come sooner rather than later, as Chapman is now analyzing the DNA of an offspring from yet another suspected virgin shark birth.
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Korean Cloned Human Cells Were Product of "Virgin Birth". Fraudulent cloned cells were likely the first example of a human egg turned directly into stem cells By JR Minkel:
Researchers say they have confirmed suspicions that embryonic stem cells claimed to be extracted from the first cloned human embryo by discredited South Korean scientist Woo Suk Hwang actually owe their existence to parthenogenesis, a process in which egg cells give rise to embryos without being fertilized by sperm.
A series of genetic markers sprinkled throughout the cells' chromosomes show the same pattern found in parthenogenetic mice as opposed to cloned mice, according to a report published online today in the journal Cell Stem Cell.
The result suggests that, although Hwang deceived the world about achieving the first human cloning, his group was first to succeed in performing human parthenogenesis, which may offer a way of creating cells that are genetically matched to a woman for transplantation back into her body to treat degenerative diseases.
"I think this is an extremely important—and solid—paper," says stem cell researcher Robert Lanza, vice president of research and scientific development at Applied Cell Technology, a regenerative medicine company headquartered in Alameda, Calif., who did not take part in the study. "It conclusively proves that the stem cell line in question was not cloned as claimed, but rather was generated through parthenogenesis."
The result follows on the heels of an announcement last month by another California stem cell company, International Stem Cell Corporation (ISC) in Oceanside, that it had successfully achieved human parthenogenesis for the first time. Last year, Italian researchers claimed to have achieved the same feat but have yet to publish their results.
"The fact that this has now been achieved by two independent groups gives me a far greater degree of confidence," Lanza says.
The new finding brings a measure of closure to a story that first rocked the science world in February 2004, when Hwang and colleagues at Seoul National University announced they had cloned a female donor's cell by transferring its nucleus into one of her egg cells stripped of its nucleus in a procedure known as somatic cell nuclear transfer (SCNT), and harvested embryonic stem cells from the resulting fusion. They published the result the next month in Science.
The claim went up in smoke in January of 2006 after a probe by the university concluded that Hwang had fabricated the evidence, which followed a similarly damning assessment of a landmark paper from the previous year in which the group falsely reported creating 11 cell lines genetically matched to their donors.
Unsolved Mysteries
A cloned cell should be identical to its donor, but the probe found that of 48 common genetic variations, or markers, present in the 2004 cells, eight did not match their apparent donor. Investigators raised parthenogenesis as the most likely explanation but could not be certain.
Later, during a chance discussion with European colleagues, stem cell researcher George Daley of Children's Hospital Boston and the Harvard Stem Cell Institute learned that they had received samples of the cell line before the work was retracted. "We had read the suspicions that the cell was a parthenote, but also realized that it had never really been proven," Daley says.
To settle the case, they analyzed the genetic sequence of the cell line at 500,000 locations across the genome.
The DNA of any two people will differ on average at one of every 1,000 subunits, or base pairs, Daley says. When a chromosome from a sperm cell joins with that of an egg, these single nucleotide polymorphisms (SNPs or "snips") tend not to match each other.
The same goes for cloned cells. But in contrast, pairs of matching chromosomes in parthenogenetic cells tend to match one another in the middle and differ near the ends because of a genetic mixing process called recombination. In their paper, Daley and colleagues report that the SNPs in the Korean cell line do indeed match toward the center of the chromosomes, similar to five parthenogenetic mouse cell lines that the team created for comparison.
In a separate analysis, they also found that three regions lacked the chemical modifications, or imprinting, that paternal genes impose on a fertilized embryo to prevent those genes from being activated.
Jeffrey Janus, president and director of research for ISC, agrees that "Dr. Hwang's cells have characteristics found in parthenogenetic cells" but remains cautious, saying "it needs more study."
The Irony of It All
Stem cell experts say that Hwang and his team probably had no clue what they had achieved, because if they had they would have claimed credit for it.
"I think this … is every bit as exciting as the SCNT they were claiming," says stem cell researcher Kent Vrana of Pennsylvania State University, who pioneered parthenogenesis in monkeys. "Parthenotes by their very nature are nonviable embryos, so you're not destroying embryos, which has some ethical advantages."
Vrana says the Korean team used a procedure common in attempts to induce parthenogenesis and SCNT alike, in which they injected egg cells with calcium and a protein synthesis inhibitor to mimic what happens when sperm fertilizes an egg.
To achieve SCNT, they first had to extract each egg's DNA and then inject the donor cell nucleus. Daley says the Korean scientists must have inadvertently left the DNA intact in one of the 242 egg cells they injected. "They claimed they verified the removal of the DNA,'' Daley says, "but obviously they didn't."
The injection of the donor nucleus could have failed if the injecting needle pulled it back out when withdrawn from the egg or if the egg somehow rejected the introduced nucleus, Vrana says.
Hwang's group purported to rule out parthenogenesis as an explanation in part by showing that two genes normally activated by paternal DNA were inactive in the cells. But Daley says such experiments are easy to misinterpret and are less conclusive than sequencing SNPs.
"I think they were just so blinded by what they hoped to accomplish, they missed it," Vrana says.
As a result, in late June, more than a year after Science retracted the 2004 paper, researchers at ISC were able to claim the discovery of human parthenogenetic cell lines as their own in the journal Cloning and Stem Cells. The group reported growing multiple parthenogenetic embryonic stem cell lines by incubating eggs in a warm, low-oxygen culture medium.
Before today's announcement, the work was already "awfully convincing," Vrana says, and surprisingly successful: out of some 50 donated eggs, the company grew six cell lines. Parthenogenesis in monkeys typically works only once every 90 eggs, he says.
Banking on Parthenotes
The therapeutic potential of parthenogenetic cells remains to be seen. The lack of imprinting from the paternal DNA may cause the cells to behave abnormally as they develop. Furthermore, they must have matching immune proteins to be transplanted back into a donor.
In principle, tissue banks of parthenogenetic cell lines could include enough different immune protein combinations to treat up to half of the U.S. population—men as well as women—Lanza says. But he adds that if human parthenotes routinely contain as many genetic mismatches as the Korean cells, the number of eggs needed to create such a bank could be prohibitively large.
Daley says his group hopes to acquire donated eggs from women with inherited diseases and use parthenogenesis to create cell lines to study those disorders. In the future, researchers will have to determine whether similar cells are safe and effective when transplanted.
"We're a long, long way," Daley says, "from realizing therapeutic uses of these cells."
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Virgin Births Lead to Transplantable Stem Cells. Stem cells created from unfertilized mice eggs are successfully transplanted without immune rejection By JR Minkel:
In the future individual egg cells may serve as the source for stem cells that doctors can transplant back into people if necessary to treat nerve damage and debilitating diseases, if researchers can extend a new procedure used on mice for making transplantable stem cells.
"This is just a small step along the way, but it's an important one," says stem cell researcher Paul Lerou of Children's Hospital Boston and Boston's Brigham and Women's Hospital. Lerou and his colleagues extracted stem cells from embryolike clusters of cells grown from the unfertilized eggs of female mice that the researchers coaxed into dividing. They injected the stem cells back into related mice, where they grew without being rejected by immune cells, the group reports in a paper published online December 14 by Science.
In principle the method could make it easier to create human stem cells and potentially carry out still far-off treatments for spinal cord injuries and degenerative diseases such as Alzheimer's and Parkinson's. "I think it's very attractive and this paper shows it has the potential to do really great things," says molecular biologist Kent Vrana of Penn State University.
Researchers have previously proposed growing embryonic stem cells using so-called therapeutic cloning, in which the nucleus of a donor's body cell is placed in an egg cell stripped of its nucleus. The problem is that the process would likely require at least 100 donated egg cells to work even once, judging from the number of eggs needed to clone animals.
To avoid this, Lerou's team in essence tricked unfertilized egg cells from mice into dividing the same way that a growing embryo would. Researchers induce this effect, called parthenogenesis, by exposing ovulating or immature eggs to a chemical that prevents them from splitting their two sets of chromosomes into two daughter cells with one set each. The process works about 70 percent of the time in mice and nonhuman primates, Lerou says.
Normally, such cells would be genetically mismatched with cells like those of their donor. Specifically, the donor would have genes for two different proteins called major histocompatibility complexes (MHC), one on each chromosome 17 in its genome. The so-called parthenote embryo, however, would have identical pairs of chromosomes, so it would have only one MHC. If a cell's MHCs do not match those of the rest of the organism, the immune system will attack and reject those cells in much the same way it rejects a transplanted organ that comes from an incompatible donor.
A parthenote's chromosomes are not completely identical, however. An egg cell starts off containing both sets of chromosomes, each of which is copied and one of which then gets expelled. Before that expulsion, the different chromosomes mix together a bit so that a chromosome that would normally have one MHC protein sometimes gets the other one instead, giving the parthenote two different MHCs.
The researchers hypothesized that they could make compatible matches if they were able to isolate the few cells in the bunch with both MHCs. Toward that end, they analyzed the genomes of individual cells from their parthenotes and, lo and behold, found a few with both proteins. When they transplanted those cells into mice that also had a mixed set of MHC proteins, the parthenote cells took hold and grew into the three major kinds of embryonic tissue.
"It's pretty solid data," says stem cell researcher Jose Cibelli of Michigan State University. "If that is going to hold true in humans we don't know, but it is very encouraging." He cautions, however, that stem cells of any origin must still prove stable when transplanted to hold any hope of treating disease. One possible hitch: Parthenotes might not grow properly, because they lack important contributions from male genes.
These articles are not in anyway written by me
