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Parthenogenesis
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by kacz on December 21, 2006
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It’s fascinating that Komodo Dragons can reproduce by parthenogenesis (see link). But the article states that the progeny will all be males! I thought that the lack of a Y chromosome would yield all females. They also mention a parthenogenic python. Does anyone know which one it is? I suspect this will get people looking for, and finding, more species of fatherless herps.
http://news.nationalgeographic.com/news/2006/12/061220-virgin-dragons.html
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RE: Parthenogenesis
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by Cro on December 21, 2006
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Paul, when I posted the link to the article on Parthenogenesis in Komodo Dragons, I was thinking the same thing, that they had made a mistake.
Usually, a Parthenogenetic animal produces all females.
Morning Geckos are known for this, as are some fishes.
I have been trying to find further information, but for now, I think they just made a typo in the article, and that it should have said that they produce all females.
Best Regards JohnZ
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RE: Parthenogenesis
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by Cro on December 21, 2006
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As far as the Parthenogenetic Python, it was a Burmese Python in the Artis Zoo in Amsterdam.
There are Worm Snakes native to India that are also known to be Parthenogenic.
Many articles describe offspring of a Parthenogenic parent as "Clones" of the parent, but I am not sure this is right. I believe that the offspring only recieve half of the geneology of the parent, thus making them a "Half-Clone" or something similar.
It seems that if males are not available, that females have the ability to produce offspring without them, to keep the species going.
I have even heard theories that human males will eventually become obsolete, as soon as human females learn to produce this trait, LOL !
Hopefully, someone who is up to date on on Parthenogenetic reproduction will weigh in on this topic, as I am way out of date on Genetics.
Best Regards JohnZ
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RE: Parthenogenesis
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by Cro on December 21, 2006
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Wow, perhaps the article was right after all. I searched Google and found this:
http://en.wikipedia.org/wiki/Parthenogenesis
This article would suggest that the production of males is a possibility in Komodo Dragons, which I guess would make sense, if there were no males available for the females, that they would create some.
This gets more and more strange.
Best Regards JohnZ
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RE: Parthenogenesis
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by Cro on December 21, 2006
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New feeds are coming in on the Komodos. It seems that one of the lizards that laid eggs, was with a male 2 years ago. So, I am somewhat skeptical again. They said:
"She arrived at London on loan from Thoiry Zoo in France last year and the clutch of eggs was laid more than two years since she had last lived with Thoiry's male, Kimaan, demonstrating that Komodo dragons can switch between asexual and sexual reproduction depending on the availability of a mate."
Perhaps she did not "switch between asexual and sexual reproduction," but simply stored sperm from the male from two years before? We know that can happen in snakes.
Stay tuned.
Best Regards JohnZ
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RE: Parthenogenesis
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by rabbitsmcgatess on December 21, 2006
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The other Komodo Dragon female had no contact with a male in her life though, wasn't it?
Also, in birds the females have the equivalent of the Y chromosome, the opposite of mammals. So if Komodo Dragons have that sort of arrangement then it would be the opposite of what you would expect in mammals.
A real stretch is that unfertilized bee eggs grow into males.
I have only ever heard of reptile parthenogenesis resulting in all-female lizards (Mediterranean [or is it Turkish?] Geckos) or snakes (Brahminy snakes).
I would love to have some parthenogenic snakes and lizards. It would be really interesting to me.
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RE: Parthenogenesis
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by kacz on December 21, 2006
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It seems that in rotifers (a type of zooplankton) parthenogenesis is both common and diverse. The females can produce diploid parethenogenic offspring that are female, as well as haploid offspring that are male! The haploid males can then contribute their haploid gametes directly to other females, whose diploid zygotes have undergone meiosis to form the other set of haploid gametes. This results in normal sexual reproduction.
If this holds true for the dragons, it infers that the females oocytes go through a meiotic division to form haploid males. In order to form diploid females the oocytes would have to bypass meiosis and form mature eggs directly.
But this doesn’t explain why the haploid gametes are male, and are they necessarily male? This is getting more confusing, and my brain’s starting to hurt!
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RE: Parthenogenesis
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by LarryDFishel on December 21, 2006
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Cro, like rabbit says, my understanding is that not all animals carry their sex genes in the same place. I don't remember if this can be different between different species of lizard.
Also, my understanding from another article I read was that after this one female laid without ever mating, they went back and checked the DNA of the offspring of the other female that they had previously thought used stored sperm and found them to be "fatherless".
As far as the parthenogenic "clones", I suspect that you're right about animals that only do this occasionally. But I would guess that things like the brahminy blind snake that reproduce ONLY parthenogenically would lose all recessive genes in a couple of generations and any given line would essentially be clones from that point on (give or take a random mutation here and there). I also suspect that one line would probably have out-competed all the others fairly early on.
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RE: Parthenogenesis
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by Cro on December 21, 2006
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Larry, I agree that "Parthenotenit Clones" would start out with half the genes of the parent, and over several generations, become closer and closer to the genotype of the parent, and thus become closer to being a clone of the first in the line that started Parthenogenesis. After a while, they would identical, for all practacle purposes.
Here is part of what I found on the web, which explains that Komodo Dragons use W and Z chromasomes, instead of the X an Y chromosomes we are used to.
"the Komodo dragon which normally reproduces sexually was found to also be able to reproduce asexually by parthenogenesis. [3] Because of the genetics of sex determination in Komodo Dragons uses the WZ system (where WZ is female, ZZ is male, WW is inviable) the offspring of this process will be ZZ (male) or WW (inviable), with no WZ females being born. A case has been documented of a Komodo Dragon switching back to sexual reproduction after a parthenogenetic event. [4]. It has been postulated that this gives an advantage to colonisation of islands, where a single female could theoretically have male offspring asexually, then switch to sexual reproduction to maintain higher level of genetic diversity than asexual reproduction alone can generate. [5] Parthenogenesis may also occur when males and females are both present, as the wild Komodo dragon population is approximately 75 per cent male."
I still wonder if 2 years seperate from a male is enough for the London Zoo to decide that a Virgin Birth had occured. I would much prefer seeing a female Komodo Dragon that had Never been with a male give birth !
What I wonder is, if female Komodo Dragons could reproduce without males, why they would produce male offspring. Why not keep on making females like Morning Geckos do? Why re-introduce males? Other than genetic diversity, what purpose do males serve? Mutations in a all female population could also account for evolution toward more survival and hardy states.
Look at Rosy O`Donnel, Jane Fonda, Sally Struthers, Ellen D`Generus and Hillory Clinton ! If they could reproduce themsleves by Parthenogenesis without males, they shurely would, LOL ! They sure would not produce males, but instead make little clones of themselves. It is a good thing that Parthenogenesis does not work in humans yet, LOL!
Bet that last paragraph upset some folks.
Best Regards JohnZ
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RE: Parthenogenesis
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by kacz on December 22, 2006
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John, I would think that genetic diversity would be enough of an incentive to re-establish sexual reproduction in the dragons. Assuming that they are colonizing a brand new (to them) ecosystem, they would benefit from maximizing their adaptability. In oogenesis (development of the ovum) there is some mixing of the chromosome segments during meiotic division of the oocytes. This would account for some diversity in the offspring, but your still restricted to the same basic genetic constituency of the female in all the progeny. Through mutation one lineage may eventually adapt better and become dominant. In essence you would have a closed system with direct linear paths with no intermixing of external beneficial adaptations.
With the advent of sexual reproduction lineages that have become diverse would be able to mix and match with the potential of some of the offspring benefiting from the beneficial adaptations of several lineages (or at least two to start). Sexual reproduction may be a much more efficient way of ensuring genetic diversity and adaptability. This is based on sketchy memories of embryogenesis and genetics courses from 30 years ago, so don’t quote me on any of this!
Another thing that intrigues me is your quoted point [5]. I don’t necessarily see the cause and effect that is postulated. Since dragons are communal feeders couldn’t it be beneficial to have a large male population if egg laying and guarding (I don’t know if they do) is particularly stressful on the females? It may have nothing to do with parthenogenesis.
As far as your last statement is concerned the thought of these people reproducing parthenogenetically is more scary, but less digusting than the traditional method!
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