Polar Bodies (Oogenesis)

[MedPR]

The primary oocyte (2n) undergoes meiosis 1 and creates a polar body as well as a secondary oocyte 👎. Then, the secondary oocyte undergoes meiosis 2, producing the ovum (2n) and the second polar body.

So it seems that both polar bodies are haploid. What would happen if a sperm fertilized one of the polar bodies?

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[chiddler]

wait, i might be wrong. rereading notes.

 

[chiddler]

polar bodies contain half the DNA "but no cytoplasm or organelles". So not much will happen even if it can. That aside, i'm sure there are some enzymatic interactions that enable the entry of sperm DNA into the egg. The polar body probably does not have those either.

 

[MedPR]

It can't. Because the polar bodies are not where fertilization happens. What I mean is he mature oocyte is not in the same location as the polar bodies.

uh...where does fertilization happen again? the fallopian tubes?

Yes, in the fallopian tubes. Primary oocyte is ejected from the follicle (in the ovary) into the abdominal cavity as a secondary oocyte. I'm assuming the first polar body goes out into the body cavity as well. Fimbriae move the secondary oocyte into the fallopian tube. I doubt they are selective, so that's why I figured the first polar body might end up in there as well.

Then the sperm comes along and fertilizes the secondary oocyte. Upon fertilization, the cortical reaction occurs, which prevents additional sperm from fertilizing the now fertilized secondary oocyte. Following the cortical rxn, the egg completes the second meiotic division (remember, the secondary oocyte is suspended in metaphase II) resulting in the second polar body.

So, even if the first polar body doesn't make it into the fallopian tube, there is still a second polar body, which presumably is a haploid cell since meiosis 2 is the same as mitosis. So what's stopping sperm from fertilizing the second polar body?

 

[MedPR]

polar bodies contain half the DNA "but no cytoplasm or organelles". So not much will happen even if it can. That aside, i'm sure there are some enzymatic interactions that enable the entry of sperm DNA into the egg. The polar body probably does not have those either.

Oh, I didn't know they didn't have organelles. Also, as far as I know, the acrosome is solely responsible for penetration. The egg doesn't "help" the sperm at all except for preventing other sperms from fertilizing.

 

[chiddler]

Yes, in the fallopian tubes. Primary oocyte is ejected from the follicle (in the ovary) into the abdominal cavity as a secondary oocyte. I'm assuming the first polar body goes out into the body cavity as well. Fimbriae move the secondary oocyte into the fallopian tube. I doubt they are selective, so that's why I figured the first polar body might end up in there as well.

Then the sperm comes along and fertilizes the secondary oocyte. Upon fertilization, the cortical reaction occurs, which prevents additional sperm from fertilizing the now fertilized secondary oocyte. Following the cortical rxn, the egg completes the second meiotic division (remember, the secondary oocyte is suspended in metaphase II) resulting in the second polar body.

So, even if the first polar body doesn't make it into the fallopian tube, there is still a second polar body, which presumably is a haploid cell since meiosis 2 is the same as mitosis. So what's stopping sperm from fertilizing the second polar body?

The first polar body is produced prior to fertilization. Then the first polar body is separated from the oocyte when the follicle bursts and the ovary is sent to the fallopian tubes.

This right?

 

[MedPR]

The first polar body is produced prior to fertilization. Then the first polar body is separated from the oocyte when the follicle bursts and the ovary is sent to the fallopian tubes.

This right?

Yes, the first polar body is produced prior to fertilization, but the ovary doesn't go into the fallopian tube. The secondary oocyte and the first polar body are ejected from the ovary into the ventral body cavity. The secondary oocyte then makes its way into the fallopian tube, a process that is facilitated by the fimbriae of the fallopian tube.

I don't really if the first polar body is actually ejected along with the secondary oocyte, or if it is just produced and then degraded within the follicle.

Prior to ovulation (pre-LH surge) the primary oocyte develops within the ovary (zona pellucida, granulosa cells, theca cells, etc) and then upon ovluation completes meiosis 1 resulting in a secondary oocyte and first polar body. The secondary oocyte is ejected (maybe the first polar body too, i'm not sure) from the ovary.

 

[chiddler]

that was a mistake. of course the ovary isn't sent to the fallopian tubes lol

 

[folktale]

There are two polar bodies produced after Meiosis II, correct? This means that there are a total of three polar bodies if you add the first polar body from Meiosis I.

EDIT: I meant the first polar body divides to form TWO polar bodies, while the secondary oocyte divides to form the ovum AND another polar body, resulting in a total of 3 polar bodies.

 

[chiddler]

There are two polar bodies produced after Meiosis II, correct? This means that there are a total of three polar bodies if you add the first polar body from Meiosis I.

There are a total of two.

1, cell

2*, polar body, and 2, primary oocyte. polar body does not divide, only primary oocyte.

3* second polar body, and 3* secondary oocyte.

edit: no polar bodies do not divide.

 

[MedPR]

Sometimes the first polar body undergoes meiosis 2. So sometimes there are 3, but I don't think that is important. Only 1 polar body is ejected at a time, and only 2 polar bodies total result directly from oocytes.

 

[folktale]

There are a total of two.

1, cell

2*, polar body, and 2, primary oocyte. polar body does not divide, only primary oocyte.

3* second polar body, and 3* secondary oocyte.

edit: no polar bodies do not divide.

I am currently looking at EK Bio page 49 and it shows a diagram of the first polar body dividing into two polar bodies.

 

[chiddler]

I am currently looking at EK Bio page 49 and it shows a diagram of the first polar body dividing into two polar bodies.

oh damn! how can they do that if it's just nucleus and no organelles!! isn't an MTOC required?

 

[folktale]

And since we're on the topic, might as well throw a question:

What phase is oogenesis suspended in before a girl reaches their menstruation age? If I remember correctly, it was in metaphase of Meiosis I? And what phase is it stuck in after ovulation prior to fertilization?

 

[chiddler]

And since we're on the topic, might as well throw a question:

What phase is oogenesis suspended in before a girl reaches their menstruation age? If I remember correctly, it was in metaphase of Meiosis I? And what phase is it stuck in after ovulation prior to fertilization?

the answer is in this thread somewhere above. it's metaphase meiosis 2.

 

[MedPR]

And since we're on the topic, might as well throw a question:

What phase is oogenesis suspended in before a girl reaches their menstruation age? If I remember correctly, it was in metaphase of Meiosis I? And what phase is it stuck in after ovulation prior to fertilization?

primary oocyte suspended in prophase 1

secondary oocyte suspended in metaphase 2

 

[folktale]

So for a pre-menstrual girl, the primary oocyte is suspended in Prophase I. For a post-ovulation pre-fertilization, it is suspended as secondary oocyte in metaphase 2? Correct?

 

[MedPR]

So for a pre-menstrual girl, the primary oocyte is suspended in Prophase I. For a post-ovulation pre-fertilization, it is suspended as secondary oocyte in metaphase 2? Correct?

Yes