Dear Annette and Gwen,

More Details on research into just One genetically-induced Form of Intersexuality may be found here:

http://www.sciencedaily.com/releases/2010/12/101202141908.htm

This follows up a family (or 2 families) in New Zealand and in France. Now this is only ONE form and cause of Intersex conditons - there are many others. This one is rare.

Some other people are born Intersexed because they are Chimeras. - where two foetae or cells from the mother have fused and formed into one foetus in the womb, long before birth. Mostly this is a just few cells mixed in with the main group, having a different genetic identity. A common sign of this is where a person has mainly dark hair and just a patch of blond or white on the head (this is called a Microchimera). Less common is when not two different foetae not only fuse, but at such an early stage that the mixture of different cell genotypes are distributed evenly through the whole foetus. Quite a few such cases manage to survive beyond birth, and even to grow up fairly normal and live interesting and successful lives. One estimate is that there may be as many as 3000 such people around now, worldwide.

Another common enough event is the crossover of genes from an X or a Y chromosome to the other one during Mitosis
(the separating of paired chromosomes into single sets for forming ovae or spermataozoa, the "sex cells") the paired chromosomes are normally coiled and tangled together, and when they separate, the paired regions sometimes break and rejoin to the other member of the pair, or can even just get doubled up on one and missing from the other. Some parts of the Y and X chromosomes do have actual paired genes, and those regions do cross over and can drag the actual sex determinant genes that were inherited from the one parent across to the other chromosome, so that an X chromosome can contain a gene that promotes a male characteristic, and a Y can grab and include one that promotes developing a female characteristic. During the "un-pairing" process it is normal for lots of exchange of material from one chromosome to another to take place, and the X and Y chromosomes are no exceptions to this.

There is a lot of randomness built into the whole process, which is why all humans are so different from eachother, and is one of the basic mechanisms of evolution - the other is the survival of the fittest part - most really mixed up combinations just do not survive even to be born alive. Of interest is also that the Y chromosome in Humans has apparently gotten smaller and carries fewer genes than it did earlier in our species's history! It is not unknown for, over an evolutionary period, a group of species to lose their original sex determining chromosomes and for new ones take over the function! Of note is that in chickens there is no y chromosome, and absence of the second x causes the egg to hatch into a cockeral !

There can be no chances of any species getting better at whatever it does, it seems, without Nature making lots of "MISTAKES" as well!

I hope this is interesting for you both, and for anyone else reading this. I was stimulated to learn all about these things for very obvious and personal reasons.

Briar