00:02
So when were talking
about gamete formation
in the female,
this is referred
to as oogenesis.
00:10
Oogenesis is the production
of female gametes.
00:14
This can take years to complete
and begins in the fetal period.
00:21
Starting with the oogonia,
which are diploid
ovarian stem cells.
00:27
These are going to multiply
many times by way of mitosis
and also store nutrients.
00:34
From there,
we will develop primary oocytes
and a primordial follicle
that will become surrounded
by follicular cells
or follicle cells.
00:47
During fetal development,
the primary oocytes
will begin meiosis,
but they will stall and that
first step of prophase 1.
00:58
It is presumed that at birth,
females contain most
of the primary oocytes
that they will have
in their lifetime.
01:09
So after puberty begins,
each month a few primary oocytes
are going to become activated.
01:17
One of these activated
primary oocytes
will become the
dominant follicle
that will resume meiosis 1.
01:26
Recall, it's been arrested in
prophase 1 since fetal development.
01:33
After puberty,
the division of meiosis 1
is going to be completed
and we get two haploid
cells of different sizes.
01:43
The first is going to be
the larger secondary oocyte
which is going to contain almost
all of the mothers cell
cytoplasm and organelles.
01:54
The second is going to
be a smaller polar body
or the first polar body.
02:00
This is going to be
a very small cell
that is pretty much devoid
of any cytoplasm at all.
02:07
This will sometimes
later degenerate
or it may divide and then
degenerate after it divides.
02:16
The second oocyte
is going to arrest
in metaphase 2
and becomes the ovulated ovum.
02:25
If the ovum is not penetrated by
sperm it will then deteriorate.
02:31
However, if fertilization occurs
and it is penetrated
by the sperm,
the secondary oocyte
will complete meiosis 2
yielding a functional
gametes or an ovum
and as well a second polar body.
02:48
Again, this polar body will
eventually disintegrate.
02:54
So if we compare
oogenesis which occurs in the
females to spermatogenesis
which occurs in the male
we find that the number
of functional gametes
that are produced
in each differ.
03:08
In oogenesis,
we only produce one viable
ovum and three polar bodies.
03:17
This is due to
unequal divisions,
which ensure that the oocyte is
going to have ample nutrients
for the six to seven day
journey that it must take
from the ovaries to the uterus.
03:31
The polar bodies are the
smaller cells that are formed
will degenerate and die.
03:38
This is an opposition
to spermatogenesis
where we produce
for viable sperm.
03:47
Along with a difference in the
functional gametes that are produced,
there's also differences
in error rates.
03:54
Spermatogenesis has an error rate
of about three to four percent,
but in oogenesis,
the error rate is
much higher at 20%.