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cladograms

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cladograms

Postby leeroykincaid » Tue Feb 25, 2014 8:09 pm

Here is a task: Look at the picture - you see three DNA sequences from three species that are related. Based on that sequence only, draw a cladogram that best represents their relatedness.

http://i59.tinypic.com/2jbmgax.jpg


My thoughts:
Since species 1 and 2 are the least related, and 2 and 3 most related, the corrct diagrams should be:
B,C,D
In fact, all three of the mentioned cladograms (B,C,D) show the very same thing.
Am I mistaken or is it the author of the questions who says only B and D are correct?

Thanx in advance.
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Postby JackBean » Thu Feb 27, 2014 3:30 pm

No, you're right, all three are the same.
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Postby Tricho » Thu Feb 27, 2014 6:28 pm

As far as I know, they are not. In B and D there is one splitting between species 1 and 3 and 2 arised out of 3, which leads to 2 being closer related to 3 than to 1. This isn't the case for C. Here there is one splitting between 1 and 2 and 3 arised out of 2. This means that 3 is closer related to 2 than to 1.
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Postby JackBean » Thu Feb 27, 2014 7:00 pm

If 3 is closer related to 2, than 2 is closer related to 3. You misunderstand phylogenetic trees.
http://www.biolib.cz/en/main/

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Re:

Postby leeroykincaid » Thu Feb 27, 2014 7:01 pm

Tricho wrote:As far as I know, they are not. In B and D there is one splitting between species 1 and 3 and 2 arised out of 3


2 did not arise out of 3. Neither of species 1,2 and 3 was created by change of one of the species 1,2 or 3.
They just have a common ancestor (node below).
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Postby JackBean » Thu Feb 27, 2014 7:01 pm

Let's put it this way. In each case, there was firt organism A (in the very bottom). Then it split into 1 and B. Further B split into 2 and 3. And it doesn't matter how you switch the tree. All the parts are freely rotable.
http://www.biolib.cz/en/main/

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Postby Tricho » Thu Feb 27, 2014 11:01 pm

Ok, I apologize if I confused the enquirer.
I always thought that if I have a line straight through (without bends) that means that it is still the same species as it was when it split. But apparently I got that wrong.
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Postby JackBean » Fri Feb 28, 2014 3:29 pm

Yes, you were wrong. These are identical:
http://upload.wikimedia.org/wikipedia/c ... ms.svg.png
http://www.biolib.cz/en/main/

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