Embryo Research _The Economist_, 26 May 1990, p. 94
Subject: Embryo Research
_The Economist_, 26 May 1990, p. 94
A few years ago most scientists used the word "embryo" to describe the
clump of undifferentiated cells that you normally get when a human egg is
fertilised. Now, to make their work sound less controversial, the
embryologists call them "pre-embryos". There is some justification for
this, since these clumps can go on to become one full-blown embryo, two of
them, a cancerous growth, or nothing. But some people think the clumps
have souls, or at least should not be tampered with. Hence the controversy
over some recent legislation in Britain that permits research on them.
Cardinal Hume, the Catholic Archbishop of Westminster, says the law
disregards Christian morality.
One aim of such research is to avoid the birth of a seriously abnormal
baby without aborting a developing foetus. The problem, for some, is that
embryos, or pre-embryos, still get destroyed. Now Dr Marilyn Monk and Miss
Cathy Holding of the Medical Research Council's mammalian research unit in
London may have found a way to avoid Cardinal Hume's worries. They have
developed a technique which should make it possible to detect many genetic
defects in human eggs -- and so discard the eggs -- before they are
fertilised. Nobody thinks an egg has a soul.
First go back to the standard technique that this might replace or
supplement, which was developed at the Hammersmith Hospital in London. It
involves surgically removing eggs from women who are at risk of bearing a
child with a serious genetic defect, fertilising the eggs outside the body
and allowing these fertilised eggs to grow to the stage of microscopic,
featureless balls of cells. Then one cell is rmeoved from each ball for
testing. If the cell -- and therefore the early embryo from which it comes
-- is free of the defects such tests look for, then the embryo is implanted
in the mother, in the hope that it will develop normally. If it does have
a defect, the embryo is destroyed.
The alternative devised by Dr Monk and Miss Holding exploits the way
that each cell in a person's body has two sets of genes, on two sets of
chromosomes. A fertilised egg contains one set of chromosomes from the
father, and one set from the mother. To produce eggs and sperm with only
one set of chromosomes, the final division of cells in the testis and ovary
is a "reduction division", or meiosis. A cell with two sets of chromosomes
splits into an egg with one set and a small cell called a polar body which
contains the other set.
If the mother is carrying a genetic defect, only one of the two copies
of the relevant gene will be affected. After the meiotic division, one set
of chromosomes will contain the bad copy, the other will contain the good
one. So if the polar body is tested for a genetic defect, and the defect
is found, then the egg will be free of the defect. On the other hand, if
the polar body does not have the defect, then the egg will. Thus, for some
common defects at least, tests of polar bodies can reveal which eggs should
be fertilised and which discarded.
Dr Monk has already shown that polar-body tests can diagnose the
defects causing sickle-cell anemia and thalassaemia, two of the most common
genetic disorders. However, some other experts believe that the test will
be less reliable than embryo tests because less genetic material is
available. The technique will be usable for only some conditions. But it
is still likely to be attractive to women who want to avoid both the
destruction of embryos and the birth of doomed children.
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