Re: [MLUG - DISCUSSION] cloning

[Mike Miller <EMAIL:PROTECTED>]

On Thu, 5 Oct 2006, Jonathan King wrote:

> OK, so I'm guessing you're talking about camptodactyly? Where your 
> little finger is crooked and does not flex? The issue there is that some 
> cases of this are strongly genetically determined, while in other cases, 
> the genetics are less clear. The condition certainly can be inherited, 
> but I don't think it has to be. The situation is a lot more complicated 
> than (say) blood type, that's for sure.

For those who don't know about it, the best place to look up a genetic 
disease is called OMIM (Online Mendelian Inheritance in Man).  Here's what 
I find in an OMIM search of camptodactyly:

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=omim&doptcmdl=OMIM&mode=text&term=camptodactyly


> Now, a hot topic in the field these days is looking for so-called 
> endophenotypes of more complex disorders or conditions. So trying to 
> figure out the genetics behind schizophrenia is a nightmare (I think 
> concordance between identical twins is only 50%), but if you could find 
> one or more phenotypes (observable characteristics) that were more 
> easily observable yet predictive of the disorder you are studying, the 
> idea is that you might be able to make more headway. (This is not my 
> area of expertise; listen to Mike if you really want to know about this, 
> since he really and truly is an expert on this stuff.)

That's all correct.  For example, we've been interested in a trait called 
"visible nailfold capillary plexus" because it seems to be largely 
genetically controlled but it is also correlated with schizophrenia and 
some schizophrenia-like disorders.


> So there is one endophenotype that I guess has turned out to be quite 
> strong, but is still fairly mysterious and actually a bit funny. We can 
> think of left handedness as a condition that has an obvious genetic 
> component, but which has environmental influences as well, and it has 
> pretty much stumped scientists what gene or genes are involved. As it 
> turns out, one really good predictor of right-handedness is having a 
> clockwise swirl direction for the hair on your head (the midwest is a 
> great place to study this, since so many guys have buzz cuts :-)). 
> Counter-clockwise swirl direction is much less common, but apparently 
> just about 50% of these people are left handed. This has suggested to 
> some a model whereby the gene or genes that are responsible for hair 
> swirl direction play a large role in handedness determination. 
> Basically, one variant of the gene may strongly bias the situation and 
> cause clockwise hair swirl and a shift towards left hemisphere dominance 
> (and handedness is tightly coupled there) while the other variant causes 
> no such bias, so that right hemisphere dominance or no dominance occurs, 
> and left-handedness becomes more probable.  It's a fun idea, but so 
> far...not too many papers.

I believe that there is a mouse mutant that is left handed 1/2 of the 
time.  Apparently, the gene causes handedness to be determined at random. 
(I think it was handedness but it could have been another aspect of 
laterality -- the important thing is that the laterality outcome appears 
to be a random coin toss for this genotype.)  So maybe this is happening 
in people too -- a single pleitropic gene could control hair swirl pattern 
and make it so that handedness is either right handed or determined by 
"invisible coin toss" among those with clockwise hair swirls.

In homosexuality research it is now clearly established that risk of 
homosexuality in men increases with the number of older brothers, but not 
older sisters.  The interesting new twist on this is that this effect 
appears to hold only for right-handed men.  With left-handed men, risk of 
homosexuality does not increase with the number of older brothers.  That 
is weird, isn't it?


> > Most certainly, the scars I have, the crooked nose I have from a old 
> > break would not be present in a clone.
>
> Maybe your clone would be just as annoying as you and somebody would 
> break his nose, too. :-)

But that does make a serious point.  Just because something is caused by 
an environmental event doesn't mean it isn't genetically influenced. 
With the broken nose, you have to wonder if everyone when struck in the 
same way would suffer the same injury.  There may be variation in "nose 
strength" and this might be partly genetically controlled.  There is also 
the issue of risk-taking behaviors that might lead to a broken nose -- 
personality may play a role in broken noses and personality is genetically 
influenced.

Mike

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