Re: Question about sperm and egg?

On Thu, 15 Jun 2006 14:37:35 -0400 (EDT), "Perplexed in Peoria"
<jimmenegay@xxxxxxxxxxxxx> wrote:


"r norman" <NotMyRealEmail@xxxxxxxxxxxx> wrote in message news:e6phq6$lse$1@xxxxxxxxxxxxxxxxxxxxxx
On Tue, 13 Jun 2006 13:18:49 -0400 (EDT), DrBenway <DB@xxxxxxxxxxxxx>
wrote:

I wonder if you (anyone) would care to add a little about the
duration or the life cycles of sperm and egg cells

I have never been clear on the issue of the "freshness" of
egg and sperm. Since a human (all mammals?) child (both sexes) is
actually BORN with ALL the primary DUPLOID sex cells that many years
later (after puberty) split via Meiosis into the Haploid sperm and egg
cells.

I'd really appreciate a further explanation of the process's that take
place between birth and puberty to these primary sex cells.(oocytes?)
Do they reproduce themselves by standard Mitosis or are they
a finite number determined while the embryo is still in the womb?

The number of haploid cells produced by each sex is an interesting
topic even assuming 40 years x 13 cycles/year x an unusual max of 2
eggs/cycle = 1040 eggs! and much closer to half that, lets say 800
ovum in a woman's life. (If I'm correct, only 1 viable ovum per
female meiosis)

Yet males produce millions of sperm (daily?) And even if there is a
2 to 1 ratio (or is it 4 to 1?) it implies that there would need be
millions of these Duploid source cells to undergo meiosis to yield
millions of the haploid Sperm.

Apparently there is massive mitosis and meiosis in males yet I believe
I have seen it stated that the female is actually born with that fixed
finite number of primaries (no further mitosis) And these
same primaries last her entire life! (thus the incidence of birth
defects increases with a females age, eggs go stale).

What I would really like to understand is that at time of
fertilization both male and female haploid gametes are relatively
"freshly" produced by a recent meiosis, but how old, were their
respective Duploid source cells?. (pre or post puberty)

Thanks so much for any input
my apologies for any blatant mistakes, (please correct them)
Genetics or Biology where never my fields of interest until recently.
Now I find it the most incredibly fascinating of all sciences.


Different organisms work differently -- plants also produce sperm and
eggs although the seed plants modify this so that they are hidden.
But let's stick with animals.

Males produces large numbers of small, motile sperm. Females produce
many fewer because of that yolk business. The growing embryo cannot
feed itself until it hatches or develops sufficiently into a larva
that can. So the more yolk that can be crammed into each egg, the
better chances each embryo has to develop and survive. That limits
the number of eggs produces. Also animals that care for the young
limit the number of offspring by limiting egg production. We humans
produce so few eggs that it turns out that all the potential eggs are
produced before birth, arrested in an early stage of meiosis. Oddly
enough, the second meiotic cell division does not occur until AFTER
fertilization! Males continue to produce large quantities of sperm
during their adult lives, at least during the reproductive season for
most mammals. That is because the diploid germ cells that give rise
to sperm, the spermatogonia, continue to divide by mitosis during
adult life produce large numbers of primary spermatocytes. These are
the cells that divide by meiosis to produce the final sperm. Note:
After one cell divides ten times, it produces about 1000 offspring.
After twenty generations, it produces one million and after thirty it
produces one billion. Yes, it takes a lot of cells dividing to
produce all those sperm! But if each cell is, say, 10 microns in
diameter, then one million will fit in one cubic millimeter of tissue
and one billion will fit in one cubic centimeter.

The "freshness" of the cells is not an issue provided the cells are
specialized to last for long (or for short) times and that the
long-lived ones live in an appropriate environment. Bees, for
example, mate just once. (Actually with several males, but just once
in her life.) The queen bee stores the sperm internally and uses that
storage to fertilize all the eggs she will produce for the rest of her
life -- several years usually. That is, she uses the sperm to
fertilize the eggs that will become workers or other queens. The
males result from unfertilized eggs. So female bees result from
freshly divided eggs but very old sperm. Humans, as I indicated
before, result from freshly divided sperm but eggs that have newly
divided through the first meiotic cell division but before that have
just sat for the lifetime of the mother.

I found a lot of information on the timing of the development of human
eggs and sperm on the web by Googling "human oocyte development". Here
is one such page (manually recombine the URL):
http://home.comcast.net/~john.kimball1/BiologyPages/
S/Sexual_Reproduction.html#Oogenesis

Regarding your speculation regarding "stale" eggs, note that there are
many different kinds of mutations; some happen only during mitotic or
meiotic replication, and others may occur while a cell is just sitting
around being bombarded by cosmic rays. One common 'mutation' in older
women - the chromosome duplication leading to Down's syndrome - cannot
possibly happen as a direct effect of just sitting around; it has to
happen during meiotic division. And the final stages of oocyte meosis
do in fact happen just in time for ovulation. But it is quite possible
that this chromosome segregation error is more likely to occur in a
"stale" cell.


Yes, as I tried to point out the first meiotic division occurs just
before ovulation on a very "stale" diploid primary oocyte. The second
meiotic division occurs just after fertilization. The sperm nucleus
is put aside until that happens and doesn't fuse with the egg nucleus
until afterwards.


.

Relevant Pages

  • Re: Question about sperm and egg?
    ... the single haploid cell that gets fertilized by the sperm, ... The zygote, still containing the nutrient yolk, and inside the ... As the cells divide to form the embryo, ... defects increases with a females age, eggs go stale). ...
    (sci.bio.evolution)
  • Re: Question about sperm and egg?
    ... duration or the life cycles of sperm and egg cells ... actually BORN with ALL the primary DUPLOID sex cells that many years ... ovum in a woman's life. ... defects increases with a females age, eggs go stale). ...
    (sci.bio.evolution)
  • 00 de puliot si sperma de A$kie
    ... Are male eggs and female sperm on the horizon? ... and female cells into sperm. ...
    (soc.culture.romanian)
  • Re: Interview with Mayr
    ... Scientists create eggs, ... Japan and the US have produced a synthetic egg and sperm-like cells from ... sperm in the laboratory is only a decade away. ...
    (sci.bio.evolution)
  • Re: frists flip-flop...
    ... I think the debate about when "life" begins is irrelevant ... to the discussion because both the egg and the sperm are alive in every ... from the ball of cells that we call an embryo. ...
    (rec.music.phish)