Identical Twins Q? From Olivier Chocron

[Pam Snyder]

In article <4mvvvc$3dj at soleil.uvsq.fr>, Olivier Chocron
<chocron at robot.uvsq.fr> wrote:

> -- Hi all,
> 
> Thanks to (Graham Dellaire) for his answer about true twins.
> Meanwhile, I have three more questions to ask to the genetic comunity:
> 
> 1) how many genes are found in each chromosome (let say in haploid form)
> in mankind genotype? The estimate is around 100,000

Are all the human genes known? NO
> 
> 2) in how many distincts alleles each human gene can be expressed?
> I learned two but it was in basic genetics (drosophilia and bins).
humans can carry no more that 2 alleles at any loci(spot on a
chromosome).  The number of alleles that actually exist in a population
can be very numerous
> 
> 3) Can we manipulate human embryos to make two equal babies as for bovins?
When attempts have been made (and it not something that is easy to get
approval for) the cells did not survive beyond 3 divisions
> 
> Are all genes equally important or can we loose some without dramatic results?
men typically have one one copy of each gene on the X chromosome and do
fine,  If however that one copy is altered in any way they are screwed. 
Some autosomal (nonsex chromosomal) genes are like this as well.  Any
disease that is called recessive requires two abberant copies to cause the
disease.  One missing or altered allele is not sufficient to cause the
symptoms of the disease.
> 
> Thanks,
> 
> Olivier
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