paul@phs.UUCP (Paul C. Dolber) (02/18/85)
Meiotic division is known as "reduction division" since it leads
to four haploid daughter cells (normal chromosome content = diploid).
(Hmmm. Three daughter cells in the human, since the first polar body
doesn't go through the second meiotic division). In each of the two
meiotic divisions a polar body is formed, which has the least cytoplasm
of the two daughter cells of a given division. In the human, the first
polar body rapidly fragments after the first meiotic division; the
second polar body is formed only after fertilization of the ovum.
It persists only through the first few cleavages of the fertilized
ovum, then disappears. Note: the second polar body is haploid (like
spermatozoa), and the second polar body is not fertilized (and hence
never becomes diploid). As well as memory and a quick glimpse through
texts at hand indicate, the order of events is: first meiotic division
(with loss of first polar body), beginning of second meiotic division,
fertilization, completion of second meiotic division (yielding two
haploid cells, one the second polar body), then combination of
chromosomes of spermatozoon and ovum ("sister" of second polar body).
We should be as concerned over the fate of the second polar body as we
are over the fate of the umpteen million spermatozoa which don't reach
the ovum, or which "are spilled upon the ground," or which are
resorbed in the epididymis.
Regards, Paul Dolber (...duke!phs!paul).