I'm not a geneticist, only a medical student but am interested in evolution. Just to state my current stance at the moment, I believe in creation.
What I am wondering is how speciation is possible?
For the purposes of this discussion I am defining a species as two organisms who are so genetically different that if they can reproduce, then their offspring are sterile e.g. Horse + Donkey = Mule.
This is how much I understand so far:
1. One species is split into two groups due to some barrier.
2. These groups only breed within their own groups and are subjected to different pressures.
3. The variation in the gene pool means that those best suited to these pressures survive to pass on their genes to their offspring.
4. This results in two different gene pools.
It is the next step I don't understand, known as hybrid sterility:
5. For the two groups to form two separte species their gene pools have to have barriers to gene flow like horses and donkeys.
My questions:
1. Does anyone know a gene which has been shown to cause hybrid sterility between two closely related species e.g. peppered moths?
2. If a member of a the two groups does gain a mutation which confers hybrid sterility, how will he mate with any member of his isolated group in order to pass on his genes e.g. people with Down's syndrome, Klinefelter's syndrome, Turner's syndrome, etc. are all sterile? Any change in chromosome number seems to render an organism (at least humans anyway) sterile.
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