bullock at tui.lincoln.ac.nz
Tue Feb 1 22:25:17 EST 1994
I don't know how to edit different messages into one posting, si I'm afraid
I can't include the original text for reference.
Everyone is entitled to their opinion but I would hope for better informed
opinions in this forum than those I've seen on the subject of "human
cloning". There appears to be a woeful misunderstanding on the part of
students(?) at PUC on what is meant by "cloning".
No-one knows how to "create humans to their liking" still less to "their
specifications and needs". Cloning will generate an embryo with the same
potential for individualism as any other birth.
Scientists cannot "get all the right ingredients" and assemble clones, human
or otherwise (including dinosaurs). The starting point is a fertilised egg,
conceived by natural mating (which may or may not be a "love act"), by donor
insemination, or by in-vitro fertilisation.
It is unlikely that attempts to clone "defective embryos" would lead to any
better "understanding about how things work". The process is highly
inefficient and the chances of success would be worse with defective
embryos, which usually fail to develop in normal circumstances, let alone
cloning. Between 40 and 60 percent of all human natural conceptions fail to
result in a pregnancy.
Correction of the "defective pendage (sic) of DNA" is being accomplished
through gene therapy, to which cloning embryos has nothing to contribute.
I have not seen the article in Newsweek but I assume that reproducing your
pet from its stored blood could only involve transplantation into an
enucleated embryo of a nucleus from a white blood cell. Nuclear transplants
have succeeded in frogs, but not, to my knowledge, from a blood-cell nucleus.
I am not aware that the incidence of schizophrenia is higher in twins than
in the rest of the population.
Which leads into a discussion of what is meant by "cloning". Cloning is the
reproduction of an organism with the same genetic make-up as the original.
Monozygotic (identical) twins are natural clones. Cloning is accomplished
by dividing an embryo at a stage when its individual cells (blastomeres)
still have the potential to develop into a complete foetus (totipotency).
In cattle this practice is now in use commercially. The technique is known
as "embryo splitting", a more descriptive, accurate, and preferable term to
To my knowledge, there has been only one report of human embryo splitting,
in which development did not proceed beyond the very early stages of
embryogenesis. There can be little scientific interest in splitting human
embryos, but there may be some clinical applications. The success of IVF is
still low, so that preserving half the split embryos could allow a second
attempt at implantation of the same genotype if the first one fails (which
it does about 70-80% of the time). If the patient particularly desired
twins, embryo splitting could provide the possibility, albeit with low
probability, of satisfying this request.
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