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Author | Topic: All species are transitional | |||||||||||||||||||||||||||
Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
Which mice? I am not aware of any mammals that can form hybrids with novel ploidy that go on to reproduce asexually and then at some point, sexually. Mice on an island could speciate sympatrically but it would have nothing to do with sudden changes in ploidy like in plants or frogs. So mammals would never face that situation.
Are you thinking of ring species?
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NosyNed Member Posts: 8996 From: Canada Joined: |
Gee, this reminds me we haven't seen him for ages .
Message 35 And from a link in
Message 42 quote:
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
Hi ned,
Thanks for the clarification. But I see a difference in this case compared to the plant example I gave. Let me see if I can clarify. quote: The mouse populations with different karyotypes are separated. It is quite possible their karyotypes changed after they speciated i.e. not the direct cause. In the plant example, we are talking about the generation of an individual or group of individuals (from the same meotic event) that have a new ploidy and cannot mate with the parent stock within a single population. They then mate either with each other (if more than one are present) or reproduce asexually until they can mate sexually. All within one population and within a single generation. Second, the mouse example is also reduction of chromosome numbers as opposed to complete changes in ploidy as can be seen in plants with complete duplication of the genome i.e. from diploid to triploid, tetraploid etc. Sometimes, even karyotypically different animals can still produce fertile offspring. They would have to test this assumption "these would probably be infertile as proper synapsis and segregation of such different chromosomes would be difficult when the hybrids attempted to form gametes by meiosis".
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NosyNed Member Posts: 8996 From: Canada Joined: |
I agree this isn't the example I was after but it is at least related.
Wilson mentions that animals also speciate through polyploidy and I was after real examples. He doesn't supply any details. This message has been edited by NosyNed, 11-02-2005 01:38 PM
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Omnivorous Member Posts: 3978 From: Adirondackia Joined: Member Rating: 7.3 |
I ran across a proffered example last night--I believe it was bivalves. I'll see if I can find it again.
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robinrohan Inactive Member |
Anybody got a nice plain definition of "polyploidy"?
I looked it up in a dictionary; unfortunately, I couldn't understand the definition. ABE: Apparently , in these circles, "polyploidy" is an everyday word, like "please" or "thank you." "How was your day, dear?" "Well, it was rather polyploidy, to be frank." "I'm sorry to hear that." "No problem. I'll get over it." That sort of thing. This message has been edited by robinrohan, 11-02-2005 10:35 PM
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Asgara Member (Idle past 2302 days) Posts: 1783 From: Wisconsin, USA Joined: |
haploid - one copy of chromosomes
diploid - two copies (think us) polyploid - more than two copies Polyploidy - Wikipedia
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robinrohan Inactive Member |
Like having triplets?
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nwr Member Posts: 6408 From: Geneva, Illinois Joined: Member Rating: 5.1 |
Like having triplets?
Not quite the same. Your sperm are haploid, because they have only one copy of each chromosome. Your regular cells are diploid, because they have two copies of each chromosome (one from your father and one from your mother). If a cell had three copies of each chromosome, presumably that would be called triploid. Mammals are normally all diploid (excluding reproductive cells). But some plants have separate haploid and diploid phases. I think some insects do that too, but my memory is hazy. Someone will probably correct me on the details. The discussion was with circumstances where there can be more than two copies of each chromosome in cells. By the way, I really liked the way you asked your question in Message 231. It was pretty funny.
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robinrohan Inactive Member |
The discussion was with circumstances where there can be more than two copies of each chromosome in cells Thanks. I'll study it out. "Turning out pigs for creationists makes me blue and blurry."--Brad McFall
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RAZD Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: |
See several examples of speciation at
Speciation & hybridization (click) V. "Instant speciation" via polyploidy etc. Plants can speciate almost instantaneously by changing the ploidy (number of sets) of their chromosomes, accompanied by their ability to persist/disperse as "founders" via asexual reproduction. They spread vegetatively and don't necessarily have to deal with the problem of sexual reproduction for some time. In animals, less dramatically, a more rapid founder effect process (Mayr, 1942; Templeton, 1996) may sometimes be an alternative to the gradual process usually considered to dominate speciation in animals. On population genetics grounds, Slatkin (1996) argued for the potential importance of what is sometimes called "founder flush" speciation in the face of several dismissive reviews of the process. For animals, the major interest in "instant" speciation involves rapid divergence due to a few changes in major regulatory genes affecting development. Recently, however, a tetraploid rodent was discovered in South America (Gallardo et al., 1999). I suspect that few biologists would have considered this a possibility until it was reported. I think you were thinking of this tetraploid rodent - it's been discussed here before IIRC Page not found - My Kratom And Weed Bloghttp://www.cricyt.edu.ar/...S/iadiza/ojeda/grecia%202000.htm enjoy {fix link - mixed ub with html} This message has been edited by RAZD, 11*03*2005 06:49 PM by our ability to understand RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ... to share.
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Brad McFall Member (Idle past 5033 days) Posts: 3428 From: Ithaca,NY, USA Joined: |
http://EvC Forum: Paleobiogeography -->EvC Forum: Paleobiogeography etc searching "genes for horns" This message has been edited by Brad McFall, 12-04-2005 10:25 AM
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SuperNintendo Chalmers Member (Idle past 5834 days) Posts: 772 From: Bartlett, IL, USA Joined: |
What we need to realise is that we are trying to impose an arbitrary system of discrete divisions on a continuous set of elements. With species it is no different. If you translate the example of the numbers to species, you can imagine a continuous sequence of intermediates from any ancestor you'd care to start with, right up to yourself. You are the same species as your parents, and they the same as theirs. At the other end of the line, the ancestor you started with is the same species as its offspring, and they are the same species as their offspring. But if you went back far enough in the lineage so that the ancestor you start with is a tree-dwelling primate, then obviously this ancestor is not the same species as you. There must be transitionals. But wherever you look in the lineage, locally you cannot pinpoint any real transitions. That's because the transition takes place all over the lineage. Each and every one of your ancestors is a transitional. And if you have children or plan on having them, you are a transitional yourself. Great, Great post. I think the problem is what we are really talking about are population groups. All members of a population group (at least for sexually reproducing animals) are always of the same species. There is no such thing as species A giving birth to species B. There are only population groups which change over time and may also split up. So a population group is always the same species... and in fact, like Para said, Species is a just an arbitrary classification we use when looking back over time at various population groups. I liked to use the analogy of the aging process (not perfect, but I think it illustrates a good point). There is never a point in your life when you wake up and say, "wow yesterday I was a child and now I am an adolescent". However, when you look back at your life you do say, "X happened when I was a child" and "Y happened when I was an adolescent". However, in reality every single instant of your life is a different step in the aging process. I've heard many people bring up the example of dogs and how they have never speciated even though we've been breeding them for thousands of years. Do we actually know this (I really don't know the answer here)? How do we know that present day dogs could breed with dogs that lived 15 or 20 thousand years ago? They may very well be a different species using that definition
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Faith  Suspended Member (Idle past 1444 days) Posts: 35298 From: Nevada, USA Joined: |
There are only population groups which change over time and may also split up. So a population group is always the same species... and in fact, like Para said, Species is a just an arbitrary classification we use when looking back over time at various population groups. The problem with this whole idea is that whenever you split a population group, each new group, while developing new forms, loses some genetic potentials, so the idea that there can be continuous open-ended change is an illusion. Over time the processes that split populations {ABE: and produce new phenotypes} also reduce genetic diversity, which ultimately reaches a point where no further change is possible. It sounds good but it doesn't work. I believe this natural limit to change is the definition of a Kind. Yes, supposedly mutation counteracts this effect, but I think that's mostly a matter of blind faith too. This message has been edited by Faith, 12-30-2005 01:07 PM
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Coragyps Member (Idle past 734 days) Posts: 5553 From: Snyder, Texas, USA Joined: |
Over time the processes that split populations also reduce genetic diversity, which ultimately reaches a point where no further change is possible. This is blind assertion on your part, Faith. You have no data to back it up whatsoever - you can't identify where that "point" would be. Biologists, on the other hand, have whole library shelves full of examples of these splits preserved in the genes and morphology of all sorts of organisms.
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