I don't wish to make a career out of contradicting Sarah, but i believe
a hybrid is, by defininition, simply a cross between two different
"species" (as variously defined!!!) or  subspp or true-breeding
varieties (as in "hybrid wheat", which is a cross beween different
varieties of the same species).  The vast majority of animal hybrids are
infertile (for most crosses, although there may be some combinations i
have not heard of, which freqently produce fertile offspring):  If they
were able to breed readily, there would be no point in calling their
parents members of different species in the first place!!  (or would
there? what if the hybrids could breed only with each other, or with one
parent  population but not the other?  ***Does anyone know of such
cases, in ANY phylum***???)
 
        I get the "digest" version of this lively list, so please forgive if
this has been posted earlier today:  A clone is formed by inducing a
single cell's nuclear DNA to form another organism geneticlly identical
to the "parent".  This is done by mitosis- simple cell division.  In
parthenogenesis, the offspring develop from unfertilized ova, which only
contain half the DNA of the parent- they are initially haploid, produced
by mitosis - a process by which new genetic combinations are formed- so
the progeny are not all genetically the same as their mother.
**HOWEVER**, in practice, most of the time the results of both processes
would in fact BE the same, since if an organism is produced by the
duplication of a haploid cell, to form a diploid organism, it will just
have two copies of each allele (version of a gene- for example, eye
color is governed by a single gene in humans, but there are several
versions of it, which produce different eye colors
(dominance/recessiveness/co-dominance is irelevant here, so we skip
it!)), UNLESS there was a mutation during the life-span of the parent,
in which case half of its ova will contain the mutation and pass it on
to her issue, while the other half will contain the origional allele,
again duplicated.
        There appears to be sufficient genetic diversity in populations of
parthenogenic species to ensure their survival- so the question arises:
Where does this come from?  Do these spp typically have certain genes
which are more prone to mutation than usual, or what  (like increased
importance of non-nuclear DNA)?????"??????????  My knowledge ends here-
so someone else will have to pick up the ball, or most of us will remain
in the dark on this rather fascinating subject!! (unless of course i am
one of the few who are still unschooled about it??)
 
                                                                                                        Always Curious in Canada,
                                                                                                        -Ross M.