What I'm getting from the
research is that it is diploid when the
sperm meets it, but it has begun the first
stages of dividing, where all of the
chromosomes have pulled to their own half
of the cell, but it has not split yet.
When the sperm penetrates the ovum's
barrier, several things happen. First, the
barrier seals off any other sperm.
Secondly, it seems, the ovum finishes
splitting, discarding the one half and
joining the other half with the sperm.
Make any
sense?
Yes Eiri that does make sense. But it
isn't diploid, it is already haploid, it
has already gone through meiosis once to
get to the point. It does divide again
though, so you're thinking is consistent
with mine.
So it divides again after it is already
haploid? So it is haploid, then it
divides again? So it has 23 chromosomes,
then it divides again. so does that leave
11.5 chromosomes?
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Georgia59
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Posted: 09-27-07 12:11pm
"In the first division, homologous
chromosomes (e.g., the chromosome 3 pair
in the diploid cell) come together and are
then separated into different cells.
Hence, the first meiotic division
separates homologous chromosomes into two
daughter cells such that each cell has
only one copy of each chromosome. But each
of the chromosomes has already replicated
(i.e., each has two chromatids). The
second meiotic division then separates the
two sister chromatids from each other.
Consequently, each of the four cells
produced by meiosis has a single (haploid)
copy of each chromosome."
One of the four cells is the egg. The egg
is haploid.
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Posted: 09-27-07 12:44pm
No silly. It has 23 chromosomes- it
divides, and the paired chromosomes split
into 23 chromatids. There is a difference.
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Georgia59
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Posted: 09-27-07 12:48pm
Homologous chromosomes means that the
chromosome has two copies of the same
thing. So there are really only 23
chromosomes after the first meiosis, that
is, 23 trait bearing things.
The 23 chromosomes split into two sets of
23 chromatids after the second division.
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Georgia59
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Posted: 09-27-07 13:01pm
Dividing doesn't only mean halving the
number of chromosomes- since chromosomes
aren't the smallest assembly of DNA.
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Verizon-y
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Posted: 09-27-07 13:14pm
Georgia59
wrote:
So I spent like a half hour
yesterday reseraching and formulating a
response, and my post didn't post?? I
don't know what happened.
I would encourage you, future, to come at
this with a different attitude. More open,
perhaps?
I think we actually only have a conflict
of terminology, not actual biology.
Oh- I was wrong when I said the egg didn't
divide until the sperm meets it, it does
divide before that, sorry. But I'm not
retracting anything else I've said. It is
still haploid!
Oh and yes, I agree with your statement.
I'm starting to feel that our argument is
one of terminology and not science.
This is going to be hard to remember what
I read yesterday but I'll give it my best
shot-
So the primary oocyte (not yet an egg)
goes through meiosis I. It is haploid at
the end of meiosis I. So there are two
daughter cells, one is called the
secondary oocyte and the other is a polar
body. The polar body has it's share of DNA
but is mainly waste product. The secondary
oocyte will then divide to form the egg
and another waste polar body, and the
first polar body will divide into two
more. So at the end, there is one egg and
three polar bodies. BUT the primary
oocyte was already haploid after meiosis
I, with the chromosomes in pairs, and the
pairs continue to divide, forming the egg.
The egg is haploid.
Here's where I got that (with my bio book
to help me)
"They become oocytes once they enter the
stages of meiosis several months after
birth. ... The oocyte is then arrested in
the first meiotic prophase until puberty.
At puberty, between 4 to 10 follicles
begin to develop, although only 1-2 are
actually released. ... Each oocyte
finishes its first meiotic division,
creating a secondary oocyte and polar
body, which serves no further function. It
begins the next meiosis cycle and is
arrested in its second metaphase, at which
point it is released from the ovary in
ovulation. It will not finish the meiosis
cycle until it encounters the stimuli of a
sperm. "
To quote that again to make sure you got
the important part...
"Each oocyte finishes its first meiotic
division, creating a secondary oocyte and
polar body, which serves no further
function. It begins the next meiosis cycle
and is arrested in its second metaphase,
at which point it is released from the
ovary in ovulation"
The oocyte has divided once before it is
ovulated. It is haploid at this point.
However- it's chromosomes are paired, so
maybe that's why you're thinking it's
diploid? But there are only 23 chromosomes
in each daughter cell (the secondary
oocyte and the polar body)
It would help me out if you would put the
part that actually comes from your link in
quotes, so I can differentiate between
what your source is saying vs. what you
are saying. I will try to make sure I am
doing the same thing.
As for this source in this post, I have
just read it. It does not mention number
of chromosomes. It does however, say
exactly what I have been saying, that
meiosis ll is not completed until sperm
hits egg.
Quote:
At puberty,
between 4 to 10 follicles begin to
develop, although only 1-2 are actually
released. Surrounding each oocyte is a
zona pellucida, membrana granulosa, and
theca cell layer. Each oocyte finishes its
first meiotic division, creating a
secondary oocyte and polar body, which
serves no further function. It begins the
next meiosis cycle and is arrested in its
second metaphase, at which point it is
released from the ovary in ovulation.
It will
not finish the meiosis cycle until it
encounters the stimuli of a sperm.
Here are all my sources from the
beginning. The bolded parts say what I
have been saying:
Quote:
"When the sperm
first makes contact, THE OOCYTE IS STILL
DIPLOID, still only halfway through
its second meiosis. The oocyte has no
nuclear membrane at this stage; the
chromosomes are suspended within the
cytoplasm, held in position by the
spindle. The touch of the sperm on the
oocyte's outer membrane stimulates the
second meiosis to move to completion. The
second polar body is then extruded; the
remaining chromosomes acquire a new
nuclear membrane and SO FOR THE FIRST
TIME FORM A HAPLOID PRONUCLEUS." --
from "The Second Creation: Dolly and the
Age of Biological Control" by
embryologists Ian Wilmut and Keith
Campbell
If an oocyte remains unfertilized and
passes during menstruation, it dies as a
diploid cell:
Quote:
and primary
oocytes remain diploid until and unless they
are fertilized by a sperm (otherwise, they
die as diploid).
The egg and sperm do not unite their
nuclei immediately in fertilization. This
next quote states that after fertilization
has begun and after meiosis ll is
completed, what you are left with is the
haploid egg nucleus and the haploid sperm
nucleus. They will combine after the
zygote divides for the first time.
Quote:
Following completion of oocyte
meiosis,
the fertilized egg (now called a zygote)
contains two haploid nuclei (called
pronuclei), one derived from each parent.
Whereas a primary spermatocyte gives rise
to four haploid sperm cells, a primary
oocyte produces just one secondary oocyte
(the spare 46 chromosomes are dumped into
the first polar body just before
ovulation), and then one egg cell (the spare 23
chromosomes are dumped into the second
polar body after fertilization). See also
chromosomal cross-over.
http://www.jansen.co
m.au/Dictionary_MO.html
Quote:
Meiosis 2 is
terminated after rupture of the follicle
(ovulation) but only if a spermatozoon
penetrates.
[T]he
diploid oocyte, which has not yet
completed meiosis 2, must erupt from the
ovary, be passed into the woman's
fallopian tube, and be fertilized there by
a sperm before becoming haploid.
Ronan O'Rahilly and Fabiola Muller, Human
Embryology & Teratology (New York:
Wiley-Liss, 2001, p. 25. See also, William
Larsen, Human Embryology (2nd ed.) (New
York: Churchill Livingstone, 1997), pp.
3-11; also, Larsen, Essentials of Human
Embryology (New York: Churchill
Livingstone, 1998); also, Keith Moore and
T. V. N. Persaud, The Developing Human:
Clinically Oriented Embryology (6th ed.
only) (Philadelphia: W.B. Saunders
Company, 1998), pp. 18-34 (also, (7th ed.,
2003); also, Bruce M. Carlson, Human
Embryology and Developmental Biology (St.
Louis, MO: Mosby, 1994), pp.3-21.
Quote:
Completion
of meiosis II thus results in the
production of four haploid daughter cells,
each of which contains only one copy of
each chromosome.
Illustration of the process by which a
single parent diploid cell (Both
homologous chromosomes) divides to produce
four daughter haploids cells (One
homologous chromosome of the pair).
Meiosis is the type of cell division by
which germ cells (eggs and sperm) are
produced. Meiosis involves a reduction in
the amount of genetic material.
Meiosis comprises two successive nuclear
divisions with only one round of DNA
replication.
Four stages can be described for each
nuclear division.
* Interphase: Before meiosis begins,
genetic material is duplicated.
* First division of meiosis
o Prophase 1: Duplicated
chromatin condenses. Each chromosome
consists of two, closely associated sister
chromatids. Crossing-over can occur during
the latter part of this stage.
o Metaphase 1: Homologous
chromosomes align at the equatorial
plate.
o Anaphase 1: Homologous pairs
separate with sister chromatids remaining
together.
o Telophase 1: Two daughter
cells are formed with each daughter
containing only one chromosome of the
homologous pair.
* Second division of meiosis: Gamete
formation
o Prophase 2: DNA does not
replicate.
o Metaphase 2: Chromosomes align
at the equatorial plate.
o Anaphase 2: Centromeres divide
and sister chromatids migrate separately
to each pole.
o Telophase 2: Cell division is complete.
Four haploid daughter cells are obtained.
One parent cell produces four daughter
cells. Daughter cells have half the number
of chromosomes found in the original
parent cell and with crossing over, are
genetically different.
Dividing doesn't only mean
halving the number of chromosomes- since
chromosomes aren't the smallest assembly
of DNA.
So, you are saying that "dividing" in
meiosis does not mean halving the number
of chromosomes?
Tell me if you agree with this, and if you
don't, please quote something or copy from
a textbook where it says differently:
In meiosis there are two cell divisions.
In meiosis l the number of chromosomes
starts out as 92. That gets halved to
46.
At the end of meiosis ll, after the second
division, the number is halved again to
23.
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Tylanas
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Posted: 09-27-07 17:20pm
Spoons of joy! I was right!
Quote:
"When the sperm
first makes contact, THE OOCYTE IS STILL
DIPLOID, still only halfway through
its second meiosis. The oocyte has no
nuclear membrane at this stage; the
chromosomes are suspended within the
cytoplasm, held in position by the
spindle. The touch of the sperm on the
oocyte's outer membrane stimulates the
second meiosis to move to completion. The
second polar body is then extruded; the
remaining chromosomes acquire a new
nuclear membrane and SO FOR THE FIRST
TIME FORM A HAPLOID PRONUCLEUS." --
from "The Second Creation: Dolly and the
Age of Biological Control" by
embryologists Ian Wilmut and Keith
Campbell
This was th specific part I actually *got*
lol.
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nightangel73
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Posted: 09-27-07 17:38pm
what is the point of this thread?
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Georgia59
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Posted: 09-27-07 17:49pm
Future- I never disagreed that the cell
doesn't finish meiosis II until
fertilization. I was just saying it was
haploid before that.
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Georgia59
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Posted: 09-27-07 17:50pm
And anything I got from sources I did put
into quotes. If you look again, they're
there. I promise.
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Tylanas
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Posted: 09-27-07 17:56pm
nightangel73
wrote:
what is the point of this
thread?
It is to disseminate new information about
biology and reproduction. It is commonly
thought that the female's egg is already
"half" a cell when met with the sperm
which is also a "half" cell. Well, it
turns out that this isn't exactly
true.
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Tylanas
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Posted: 09-27-07 17:57pm
Georgia59
wrote:
Future- I never disagreed
that the cell doesn't finish meiosis II
until fertilization. I was just saying it
was haploid before
that.
It's in a pseudo-state. It's not fully
divided, but it's not totally one cell
still. Technically, all 46 chromosomes are
in ONE cell, so it's technically diploid.
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Georgia59
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Posted: 09-27-07 17:58pm
Yay Eiri!!
It is becoming clear to me now...
But I still stand that the problem was in
the terminology. Does haploid mean 23
chromosomes? Does it mean the DNA is in
chromatids vs. chromosomes?
When the cell first multiplies at the
beginning of meiosis I, it starts by
multiplying. It makes copies of the
chromosomes. That doesn't mean there are
92 chromosomes, it means that the original
46 has been multiplied. There are still 46
'genes' or chromosomes being expressed. So
when it splits, there are 23 chromosomes
or genes beings expressed.
There are different building blocks,
chromatids and chromosomes, each which can
represent a gene.
Does that make sense?
This is why I think we're getting
confused, but I think we have come to the
end.
It's all just the words we're using. When
I tried to find strict definitions of the
words chromosome, haploid and diploid, I
couldn't find a definition that seemed to
be agreed upon. I think it's because in
the case of oogenesis, it's really not
clear and you have to pay closer attention
to the DNA and not try to define the
chromosomes and such.
Does that make any sense? I hope this is
coming to conclusion.
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Verizon-y
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Posted: 09-27-07 21:30pm
Georgia59
wrote:
Yay Eiri!!
It is becoming clear to me now...
But I still stand that the problem was in
the terminology. Does haploid mean 23
chromosomes? Does it mean the DNA is in
chromatids vs. chromosomes?
When the cell first multiplies at the
beginning of meiosis I, it starts by
multiplying. It makes copies of the
chromosomes. That doesn't mean there are
92 chromosomes, it means that the original
46 has been multiplied. There are still 46
'genes' or chromosomes being expressed. So
when it splits, there are 23 chromosomes
or genes beings expressed.
There are different building blocks,
chromatids and chromosomes, each which can
represent a gene.
Does that make sense?
This is why I think we're getting
confused, but I think we have come to the
end.
It's all just the words we're using. When
I tried to find strict definitions of the
words chromosome, haploid and diploid, I
couldn't find a definition that seemed to
be agreed upon. I think it's because in
the case of oogenesis, it's really not
clear and you have to pay closer attention
to the DNA and not try to define the
chromosomes and such.
Does that make any sense? I hope this is
coming to
conclusion.
Eiri is not confused at all. You are just
ignoring every bit of information I am
provifing for you, and I honestly don't
know why.
And to think the ORIGINAL REASON I even
brought this up was because it provides
ammunition for our side of the
abortion debate.
Many pro-lifer's base their argument that
a fertilized egg is a human being because
it has 46 chromosomes, and it has
"everything it needs" according to them,
to build a complete person.
Pro-choicers respond sometimes by asking
why not value the egg and sperm as well?
They make babies, too. Without an egg and
sperm, there would never be a baby.
Prolifers fight back with, because sperm
and egg only have 23 chromosomes
each, so they are not human beings.
So the only reason these prolifer's value
the fertilized egg and not the sperm and
egg is because of the number of
chromosomes.
Well, after hearing that a zillion times,
I began to look into it. That's when I
found out that the prolifer's were
wrong!!!!!!!!
Does this make sense now?
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Georgia59
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Posted: 09-28-07 12:42pm
I'm perfectly willing to admit that we're
both right, but looking at the issue
differently. Why aren't you willing to
admit I'm right? I've read what you've
posted, I've read my own reserach, and the
more I look into it the more I'm seeing
that we really do have the same
information, we're just talking about it
differently. Did you read my last post at
all?
Anyway, I understand your original
argument, but that doesn't make sense
either. Sperm definitely only has 23
chromosomes, and an egg on it's own
doesn't have the information to make it's
own human being. Ever, regardless of the
number of chromosomes.
And every cell in our body has 46
chromosomes, and all the DNA that is
needed to make a baby if it were to have
the mechanical process to do it. So the
argument is moot in the first place.
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Verizon-y
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Posted: 09-28-07 13:43pm
No, we are not saying the same things.
An egg only has 23 chromosomes after it
encounters a sperm. Before that, it is a
diploid oocyte. Period, end of story.
I've given you 9 sources saying this. You
have yet to show me one source that says
an egg has 23 chromosomes BEFORE it
encounters a sperm, or even, that an egg
has 23 chromosomes after ovulation.
And you won't be able to find one, either,
because there is no such thing as an "egg
with 23 chromosomes" before a sperm meets
it.
The thing released at ovulation is a
diploid oocyte. If it is not penetrated
by a sperm, it will pass in menstruation
and die as a diploid oocyte.
The only time it becomes a haploid egg is
when it encounters a sperm.
And it is only a haploid egg for a matter
of hours, because in the process of
fertilization the haploid egg and haploid
sperm will merge to become diploid.
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Georgia59
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Posted: 09-28-07 16:36pm
"Telophase I
The first meiotic division effectively
ends when the centromeres arrive at the
poles. Each daughter cell now has half the
number of chromosomes but each chromosome
consists of a pair of chromatids."
I wiki'ed it. I know wikipedia isn't a
reliable source so you can put up a fuss
about it, but it's the same as other
things I've read and learned. Each
daughter cell has half the number of
chromosomes, so it has 23 chromosomes. But
each chromosome is a pair of chromatids,
so it can split again.
Seriously? Why are you so angry and
non-flexible on this? I'm willing to say
it's just a terminology issue. Like I
said, there is not always a clear
definition between chromosomes and
chromatids. When I say there are 23
chromosomes, there may be 46 structures,
but only 23 different trait bearing pieces
of DNA.
I'm done with this. I feel that I have
figured out the truth for myself, and
thank you for the probing into the issue
to force me to do that. I'm willing to
agree here, but if you're not, I'm done.
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Verizon-y
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Posted: 09-28-07 17:17pm
That first division is 92 to 46. The last
one is 46 to 23. I wrote it 9 different
ways, 9 different sources. How can I be
flexible here? It is what it is.
An egg cell has 23 chromosomes ONLY AFTER
IT ENCOUNTERS A SPERM.
