posted
(Caveat: If this turns into a creationism thread, I'm deleting it.)
I know we have a lot of knowledgable folks here when it comes to genetics, so I wanted to get some information.
According to this, we share on the order of 95% of our genetic material with chimps. And according to this, which granted is a few years older and may no longer be the prevailing view, we share about 99% of our genetic material with mice.
This seems odd to me. Is one of the sources wrong? Or is there a reason why this makes sense?
Posts: 12266 | Registered: Jul 2005
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posted
The second one has a very misleading quote. It is not accurate to say that we share 99% of mice's genetic material; we have approximately that many genes in common. And "in common" does not mean identical in this context; hence the word "equivalent" used several times in that article.
As opposed to the 95% figure, which is based on a side-by-side comparison, as it were.
Posts: 32919 | Registered: Mar 2003
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posted
Those look like separate measures, the second is actually, "We share 99 percent of our genes with mice..." but gives no measure as to how different our genes are in terms of mutation.
The first is a measure of mutations only since " ... he found that single base substitutions accounted for a difference of 1.4 per cent, very close to the expected figure.
But he also found that the DNA of both species was littered with indels. His comparisons revealed that they add around another 4.0 per cent to the genetic differences."
Different organisms can share genes, but those shared genes can have differing amounts of divergent mutations (Ex: http://en.wikipedia.org/wiki/BLOSUM albeit proteins, but similar idea).
Posts: 7593 | Registered: Sep 2006
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Disclaimer: Not a biologist. This is the understanding of an interested layman.
It depends on what you're counting. This sort of statistic is sometimes given as the number of protein functions we share; so you have protein A in humans which, say, reverses the polarity of the transneuron oxidizer; and you have a protein B in pumpkins which does the same job; and so we 'share' the gene for that protein even though the actual coding may be quite different. So you'll find that we share, say, 50% of our genes with a pumpkin, in this broadest possible sense.
Then there is the strictest possible sense, which is "For that part of the human genome which differs, how much is identical between these two people"? It is in this much narrower sense that (making up numbers) a Pole shares 95% of his genes with a Norwegian but only 80% with an Maori. If you were counting the whole genome the numbers would be much higher, but for this purpose it's more useful to ignore the parts that every living human shares anyway, because if you didn't share it you'd be dead.
Between these two senses of 'share' there is a continuum. With chimps, the genomes are sufficiently close that you can do a base-by-base comparison and say, "Ah-hah, here the sequence AGC was inserted/deleted/moved". Then the question is, do you count
GCTAGCTCGA GCT___TCGA
as sharing 70% of their genes, since the GCT[x]TCGA sequence is the same, or 30%, since there is a clear difference after GCT, or 0% since the protein it codes for has changed? (Noting that the protein may still perform the same function, of course.) So the difference between the mice and chimp statistic arises, probably, from this sort of interpretive issue. If the metric that was used for mice was applied to chimps, we'd share even more than 99% of our genes with the chimps.
You'll note a common pattern here: As the relation grows closer, the definition of 'share' resets so the number grows smaller; this is because it's harder to compare numbers very close to 100% than numbers that use more of the 0-100 range, so the definition is renormalised to give a more graspable range.
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So is there any indication of how the two would compare on the same scale? I mean, it's obvious that mice and rats are much more different to us than any apes, but I'd like to have some numbers I can use. You wouldn't think that'd be necessary, but it's a weird world.
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Bit of an aside, but I was just reading a story today about vaccine testing in lab animals, and how a lot of the time, the treatments we develop on mice have zero bearing on human applications, and a lot of research time ends up on the cutting room floor because we can't make the jump. As a result, recent trends in lab animal testing are moving towards using primates as test subjects for pharmaceuticals since the reactions in their biology are much more transferable. Not sure how that butts up against laws against what animals can be used as test subjects and how, but I see the argument.
Posts: 21898 | Registered: Nov 2004
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posted
No, you couldn't really put them on the same scale much, beyond the similarities with chimpanzees being much, much higher.
Pulling in an outside source that gives an idea of the genetic overlap of each pair of 'shared genes' (about 85%, though that might be averaged over genes and not length of DNA) and applying that, that would put genetic overlap with mice (on vaguely the same terms as with chimpanzees) at a tad under 85%. Pretty far away, given how recently mammals diverged from each other.
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