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Author Topic:   The Ancestor's Tale
JustinC
Member (Idle past 4843 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 1 of 7 (374317)
01-04-2007 5:37 AM


I just started reading "The Ancestor's Tale" by Dawkins and I'm having a little trouble understanding Eve's Tale. I'm assuming atleast some people on this site have read the book and can help explain this part to me.
Dawkins' discusses how we can produce a gene tree from a group of individuals. You compare a particular locus on different individuals and look for their Most Recent Common Ancestor. Depending on the particular loci, you get different gene trees. No trouble yet.
Here is the part I don't get:
Individual people who are closely related share a large number of gene trees. We share a majority of our genes with our close kin. But some gene trees deliver a 'minority,' placing us closer to our otherwise more distant relatives. We can think of closeness of kinship among people as a kind of majority vote among genes. Some of your gens vote for, say, The Queen, as a close cousin. Others argue that you are closer to seemingly much more distant individuals (as we shall see, even members of other species). When quizzed, each piece of DNA has a different view what history is all about, because each has blazed a different path through the generations. We can hope to gain a comprehensive view only by questioning a large number of genes.
Basically, I don't understand what he means by the first lines. Specifically,
Individual people who are closely related share a large number of gene trees.
This seems to imply that an individual has different unique gene trees, and that these can be compared to another individuals unique gene trees.
But how can individual make a gene tree, since you only have one data point. Aren't gene trees produced by comparing a particular loci on different individuals and looking for coalescent points all the back to the ultimate coalescent point of the group, the Most Recent Common Ancestor?
It's late and I've been up for a while so this might just be the result of my brain wearing down but I don't get it.
Can anyone explain this to me?
Book Nook, obviously.
Edited by JustinC, : No reason given.
Edited by JustinC, : No reason given.
Edited by JustinC, : No reason given.
Edited by JustinC, : Very clumsy wording

Replies to this message:
 Message 3 by Modulous, posted 01-04-2007 6:13 AM JustinC has replied

  
AdminModulous
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Message 2 of 7 (374320)
01-04-2007 6:09 AM


Thread moved here from the Proposed New Topics forum.

  
Modulous
Member
Posts: 7801
From: Manchester, UK
Joined: 05-01-2005


Message 3 of 7 (374321)
01-04-2007 6:13 AM
Reply to: Message 1 by JustinC
01-04-2007 5:37 AM


I haven't read it yet, but it looks like it makes sense. Gene trees aren't the same as family trees. You'll have a gene tree for each gene you have.
You can actually do this for yourself. If you compare a bunch of species' cytochrome c you'll get a gene tree. If you compare their haemoglobin b gene you'll get a different gene tree. You need to compare lots of genes to get an 'average' gene tree that is closest to the truth.
This works at the species level, but it can also work at the individual level.
So yes, if we get 10 related people, and we look at their gene trees - they will likely be a lot of gene trees that are very similar or identical.


Incidentally, I can see how the wording looks clumsy, but the following paragraph seems to clear up what is being said I think. I often find that is the case with his books - it looks a bit odd in one light, but with further reading it seems to make sense. In my case, the more I read the paragraph the more difficult I'm finding it to 'get'. I think the above is what he's saying, but I'll have to read the book before I can commit to it Sorry.
Edited by Modulous, : No reason given.
Edited by Modulous, : No reason given.

This message is a reply to:
 Message 1 by JustinC, posted 01-04-2007 5:37 AM JustinC has replied

Replies to this message:
 Message 4 by JustinC, posted 01-04-2007 6:41 AM Modulous has replied

  
JustinC
Member (Idle past 4843 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 4 of 7 (374323)
01-04-2007 6:41 AM
Reply to: Message 3 by Modulous
01-04-2007 6:13 AM


quote:
You can actually do this for yourself. If you compare a bunch of species' cytochrome c you'll get a gene tree. If you compare their haemoglobin b gene you'll get a different gene tree. You need to compare lots of genes to get an 'average' gene tree that is closest to the truth.
I understand this. You take the majority vote to decide which gene tree best represents reality amongst a group of species/individuals.
But how can you produce gene trees from an individual, and compare them to another individual's gene trees, and guage relationship status.
If he means what you wrote, then I think it looks like clumsly wording. [EDIT]First sentence of the paragraph that is[/EDIT]
Edited by JustinC, : No reason given.

This message is a reply to:
 Message 3 by Modulous, posted 01-04-2007 6:13 AM Modulous has replied

Replies to this message:
 Message 5 by Modulous, posted 01-04-2007 6:48 AM JustinC has replied

  
Modulous
Member
Posts: 7801
From: Manchester, UK
Joined: 05-01-2005


Message 5 of 7 (374325)
01-04-2007 6:48 AM
Reply to: Message 4 by JustinC
01-04-2007 6:41 AM


Individual people who are closely related share a large number of gene trees.
I think the plural is important here.
If we have three people and we compare gene A we might find the gene tree being:

X
Y Z
If we then compare gene B we get a gene tree of

X
Y Z
gene c:

X
Y Z
and gene D

Y
X Z
So the individual people (who are closely related) share three (out of four) gene trees.

This message is a reply to:
 Message 4 by JustinC, posted 01-04-2007 6:41 AM JustinC has replied

Replies to this message:
 Message 6 by JustinC, posted 01-04-2007 8:27 AM Modulous has not replied
 Message 7 by JustinC, posted 01-04-2007 8:29 AM Modulous has not replied

  
JustinC
Member (Idle past 4843 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 6 of 7 (374336)
01-04-2007 8:27 AM
Reply to: Message 5 by Modulous
01-04-2007 6:48 AM


I'm not quite sure how to read your gene trees since normally all the genes are on the level with lines connecting coalescent points. Can I assume that genes A,B, and C shows this tree:
Y    Z    X
|____|    |
  |_______|
      |
and gene D shows:
X    Z    Y
|____|    |
  |_______|
      |
And you're saying that since 3 out of 4 of the trees show the first tree, then that is likely the tree which accurately depicts their relationships.
If that's all he's saying then its just the wording that's throwing me off. I just bound to get hung up on small things like this and its hard for me to move on until I resolve it.
And if that is what he is saying, instead of wording it as:
So the individual people (who are closely related) share three (out of four) gene trees.
wouldn't a more accurate way be:
Three out of four trees show that Y and Z are more closely related to each other than they are to X
Thanks for the help btw!
Edited by Admin, : Fix formatting.

This message is a reply to:
 Message 5 by Modulous, posted 01-04-2007 6:48 AM Modulous has not replied

  
JustinC
Member (Idle past 4843 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 7 of 7 (374337)
01-04-2007 8:29 AM
Reply to: Message 5 by Modulous
01-04-2007 6:48 AM


Double.
And those trees didn't turn out like I thought. But hopefully you can get the gist of what I was trying to draw. For the first tree, lines from Y and Z first converge into one line, and then that line converges with a line from X.
Same type of thing for the second tree.
Edited by JustinC, : No reason given.

This message is a reply to:
 Message 5 by Modulous, posted 01-04-2007 6:48 AM Modulous has not replied

  
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