Primary spermatocyte ? from EK ICLE2

[RUc10]

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So I got this wrong, but I'm not sure if my reasoning is flawed or maybe it's bad question/explanation? Here it is:

A primary spermatocyte is:
A. haploid and contains 23 chromosomes
B. haploid and contains 46 chromosomes
C. diploid and contains 23 chromosomes
D. diploid and contains 46 chromosomes

I chose A. Reasoning was that sperm and eggs are haploid. Primary spermatocytes represent these cells after S phase of mitosis in which the DNA has already been replicated. BUT since the cells are haploid there is still at this point only 1 copy of each chromosome each consisting of 2 sister chromatids.

Book says the answer choice is D.

Am I wrong in my logic? The only way D could be true is if sperm and oocytes were diploid like somatic cells which I'm fairly certain they aren't. EXPLAINNNN por favor

 

[kehlsh]

Primary spermatocytes undergo Meiosis 1 and they are diploid. When Meiosis 1 is complete, they are called secondary spermatocytes and now they are haploid.



Below is a section from mcat-review:

1. Spermatogonium (2n) = stem cell. Mitosis of spermatogonium can either create more spermatogonium or create primary spermatocyte.
2. Spermatogonium (2n) → mitosis → primary spermatocyte (2n). Occurs after puberty.
3. Primary spermatocyte (2n) → meiosis I → Secondary spermatocyte 👎.
4. Secondary spermatocyte 👎 → meiosos II → spermatid 👎.
5. Spermatid 👎 → mature → sperm 👎. The fancy name for sperm is spermatozoa.

Hope it helped,

Kehlsh

 

[RUc10]

I'm still a little confused, sorry I'm slow. Hopefully you still check this thread or some one else can help as well.

I guess what I need answered is: what exactly is a spermatogonium? I understand that this is diploid so now I understand why the answer to the question is D. However, I thought sperm and eggs were haploid (as you mentioned in step 5). So when does a sperm become a spermatogonium and become diploid?

Further, what phase are sperm and an egg in when they combine, as far as what stage of meiosis they've undergone and number of chromosomes?

Hopefully this isn't too much, I really appreciate it. Probably something I should have remembered a long time ago 🙁

 

[PiBond]

I'm still a little confused, sorry I'm slow. Hopefully you still check this thread or some one else can help as well.

I guess what I need answered is: what exactly is a spermatogonium? I understand that this is diploid so now I understand why the answer to the question is D. However, I thought sperm and eggs were haploid (as you mentioned in step 5). So when does a sperm become a spermatogonium and become diploid?

Further, what phase are sperm and an egg in when they combine, as far as what stage of meiosis they've undergone and number of chromosomes?

Hopefully this isn't too much, I really appreciate it. Probably something I should have remembered a long time ago 🙁

Spermatogonium are the male germ cells that will be activated to primary spermatocytes who will then undergo meiosis I/II to yield our spermatids who will later mature into sperm. They are essentially going to start this process in the outer membrane of the sertoli cells and differentiate (become more sperm-like) until they reach the lumen of the seminiferous tubules.

When an egg and sperm combine, the sperm is haploid and has completed meiosis II. However the egg is a secondary oocyte (also haploid) who will only undergo the second meiotic division if fertilized.

 

[RUc10]

That actually helps a lot. I had been thinking of spermatogonium interchangeably with sperm itself.

Last question though and everything should be cleared up.

What is the meiotic process once they are combined? You're saying the egg is a secondary oocyte, so it is haploid but each chromosome still has 2 chromatids since it hasn't undergone Meiosis 2. So how does everything line up during metaphase? The haploid sperm lines up on the plate in addition to the oocyte and whichever daughter cell possesses the sperm and a chromosome (which now would only have 1 chromatid) after anaphase is the actual product of reproduction? And this cell is what multiplies? Or is it something else.

Sorry again, after that I'm good on this topic.

 

[PiBond]

That actually helps a lot. I had been thinking of spermatogonium interchangeably with sperm itself.

Last question though and everything should be cleared up.

What is the meiotic process once they are combined? You're saying the egg is a secondary oocyte, so it is haploid but each chromosome still has 2 chromatids since it hasn't undergone Meiosis 2. So how does everything line up during metaphase? The haploid sperm lines up on the plate in addition to the oocyte and whichever daughter cell possesses the sperm and a chromosome (which now would only have 1 chromatid) after anaphase is the actual product of reproduction? And this cell is what multiplies? Or is it something else.

Sorry again, after that I'm good on this topic.

when the secondary oocyte and the sperm's membrane fuse, they are considered a dikaryon (2 nuclei) for a period of time until the secondary oocyte undergoes its last meiotic division (meiosis II). meiosis II for the oocyte is just like mitosis in terms of metaphase. we're going to separate the sister chromatids, and form two new cells with DNA (ovum and second polar body). when this takes place, the egg and sperm nuclei finally fuse and form the zygote. the second polar body made from the oocyte's meiosis II is ejected. after the zygote is formed is starts its mitotic divisions and begins moving down the fallopian tubes until is reaches the uterus where it will implant.

 

[RUc10]

Thanks a lot. I appreciate it.