Rich Ulrich wrote
>>>>> sperm can be sorted by weight in a centrifuge, since sperm with
>>>>> Y-chromosomes generally weigh less than the X-chromosomes,
>>>>> by the amount of that extra arm.
Photos I've seen suggest a variation of some tens of percent in the size
of sperm - the philosophy doesn't seem to involve quality control. A
quarter-chromosome is about 1% of the size of a sperm.
Moreover, centrifuges separate not by weight but by sinking speed, which
depends
on weight, density, and shape.
_If_ this process works it is proabbaly not because of the extra arm,
but because
the shapes or mechanical properties of the X chromosomes differ from those
of the
Y chromosomes - which apparently they do, visibly.
(Similarly, if you separated adult humans by weight you would achieve
some sex selection, but not because of females being heavier by a chromosome
arm per cell..)
-Robert Dawson
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