Mitosis?

[DeathandTaxes]

---

Members do not see this ad.

If chromosomal duplication before tetrad forma-tion occurred twice during spermatogenesis, while the other steps of meiosis proceeded normally, which of the following would result from a single spermatocyte?


A One tetraploid sperm


B Four diploid sperm

C Four haploid sperm


D Eight haploid sperm

Can anyone help me visualize what's going onhere? I thought it would be either B or D based on process of elimination because C is a regular process, and A just seems weird. But I couldn't pick between these logically.

 

[quicheduty]

Hopefully it's B!
Some easy ways I used for POE:
-Spermatogenesis results in 4 spermatids, so A and D are out
-Obviously there is something going wrong in the process, and you know there is going to be too much genetic material. Since, like you said, C is the normal process, it can't be correct. C is out, and you're left with B.

Edit: For the full explanation on why B is correct I'll refer you to a previous thread I found (it explains it decently I think)
http://forums.studentdoctor.net/threads/chromosomal-duplication.505083/

 

[Czarcasm]

Seems like a strange question. It's like their baiting you to chose B and B could be correct, but personally, I'd put C. When homologous chromosomes separate during anaphase I, each chromosome is already in replicated form (hence why we have sister chromatids). A second replication event would be no different. We'd still have even more replicated DNA, but half the chromosome number.

 

[StIGMA]

B. Also, the question is about meiosis (not mitosis as in the title), if you did not realize these are different processes. 8 haploid sperm would require 3 rounds of division from an octaploid cell, not 2 as in meiosis. # = ploidy [8 > 4 > 2 (4x diploid)] (B) vs [8 > 4 > 2 (4 x diploid) > 1 (8x haploid)] (D).

The question requires you to recognize meisosis is a double-division process.

 

[Czarcasm]

B. Also, the question is about meiosis (not mitosis as in the title), if you did not realize these are different processes. 8 haploid sperm would require 3 rounds of division from an octaploid cell, not 2 as in meiosis. # = ploidy [8 > 4 > 2 (4x diploid)] (B) vs [8 > 4 > 2 (4 x diploid) > 1 (8x haploid)] (D).

The question requires you to recognize meisosis is a double-division process.

I originally thought that too, but wasn't entirely sure since I figured by the second round of division, the centromere which holds the chromatids, would be pulled apart. How exactly would it work in this instance, considering that we no longer have a centromere present after the second division?

 

[StIGMA]

I originally thought that too, but wasn't entirely sure since I figured by the second round of division, the centromere which holds the chromatids, would be pulled apart. How exactly would it work in this instance, considering that we no longer have a centromere present after the second division?

1) This is a hypothetical question. 2) There are only 2 divisions, so the last part of the question is moot. 3) There could/would still be a centromere (it can reform), which is basically a complicated protein attachment onto the centromeric DNA. You cannot assume there would not be a centromere.