From: Damien Broderick (damien@ariel.ucs.unimelb.edu.au)
Date: Fri Dec 18 1998 - 11:56:03 MST
At 11:50 PM 12/17/98 -0800, Hal wrote:
>> Can a 'clone' of yourself be manipulated to the opposite sex?
>I would guess that
>you might be able to turn a male into a female by removing the Y and
>duplicating the X (maybe borrowing an X from another cell).
No. (We did this discussion a few weeks back.) Genomic imprinting means
you need chromosomes from both sexes - even a female needs an X from mother
and an X from father. Here's why:
=======
It turns out that the impact of parental sex on inherited character is not
at all what old fashioned bigots might like to imagine. So far the results
have been demonstrated mainly in mice, but the genes involved are also
found in humans. They imply that some traits are preferentially distributed
unevenly among a couple's children. In brief, in the words of science
journalist Gail Vines: `a mother's genes play the dominant role in the
development of the parts of her offspring's brains that are responsible for
intelligence. The father's genes . . . may shape . . . the parts of their
brains that influence emotional make up'.
This news must make immensely satisfying and amusing reading to those women
who have suffered demeaning insinuations that they are surely responsible
for any nervy, hysterical emotionality in their children, while stern
fathers take credit for the keen manly intelligence that breaks through
once the brats' moods and feelings are whipped into shape and brought under
control. Quite the reverse is true, if this correlation holds up. It will
not surprise those who have noticed how many clever children have smart,
articulate mothers and quite ordinary or even lacklustre fathers.
Even before conception, genetic Darwinism is at work, labelling certain
chunks of DNA - and not just in the sex chromosomes - to mark their origin
in either mother's or father's germ cells, and to activate them only under
particular circumstances. We need imprinted genes from both sex lines,
since they do different jobs. That is one reason why radical hopes of
creating an embryo by splicing together the haploid DNA of two spermatozoa
(a baby with two genetic fathers) or two ova (a baby with two genetic
mothers) won't work without very refined gene engineering, to the chagrin
of some homosexual and lesbian couples. This, though, is not a futuristic
gay utopia scenario - it was tried in 1984 using mice sperm and ova, and
failed. In each case, a number of critical genes had been switched off in
the DNA contributed by the two fathers or two mothers, so foetal
development stalled. Mother-marked genes control early embryo growth, and
the father-marked genes kick in with later development.
What happens if extra amounts of the genomically imprinted genes are added
to the normal embryological mix, creating a chimera? Vines reports:
Embryos with an extra dose of maternal genes grew into fetal mice with big
heads (and brains) perched on small bodies. By contrast, embyros with an
extra dose of the father's genes grew into fetuses with huge bodies but
tiny brains.
Perhaps that sounds more like a coarse schoolyard cliché. Momma's boy nerds
versus pinhead jocks. When the fine grain detail was examined, the
underlying effect was even more startling. Cells with father marked genes
drifted during development into the limbic system, the `emotional' brain -
notably, the hypothalamus and amygdala - but avoided the cortex and
striatum, where fine movement is controlled. Mother marked cells made the
reverse choice, avoiding the evolutionarily more primitive regions of the
brain in favour of the newer modules where planning is generated.
Predictably, an entire book has already been published (by the perhaps
appropriately-named academic, Christopher Badcock) arguing that paternal
genes lay the groundwork for the Freudian id, repository of unconscious
drives, while maternal genes do the same for the ego, or deliberative,
conscious self. It is a notion as greedily reductionist and essentialist as
anything in the ripest days of social Darwinism. For all that, it might
contain some hint of truth.
THE LAST MORTAL GENERATION, by yr obdt. svt., forthcoming 1999.
Damien Broderick
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