Meiosis question

[Temperature101]

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When human female is born, the development of her oocytes is arrested in:

A. prophase of mitosis
B. prophase I of meiosis
C. prophase II of meiosis
D. interphase


The answer is "B". I got it by process of elimanation since the other answers do not make sense at all. However, i don't get the logic behind it. Can someone explain it to me in detail.

 

[MT Headed]

I don't think it's logical. It's a discrete trivia question related to how human beings actually function.

 

[HoltMD]

When human female is born, the development of her oocytes is arrested in:

A. prophase of mitosis
B. prophase I of meiosis
C. prophase II of meiosis
D. interphase


The answer is "B". I got it by process of elimanation since the other answers do not make sense at all. However, i don't get the logic behind it. Can someone explain it to me in detail.

The answer is 'C'.


"Oocytes of different species vary as to when meiosis resumes and fertilization takes place. In some animals, oocytes remain arrested at the diplotene stage until they are fertilized, only then proceeding to complete meiosis. However, the oocytes of most vertebrates (including frogs, mice, and humans) resume meiosis in response to hormonal stimulation and proceed through meiosis I prior to fertilization. Cell division following meiosis I is asymmetric, resulting in the production of a small polar body and an oocyte that retains its large size. The oocyte then proceeds to enter meiosis II without having re-formed a nucleus or decondensed its chromosomes. Most vertebrate oocytes are then arrested again at metaphase II, where they remain until fertilization."

Source: http://www.ncbi.nlm.nih.gov/books/NBK9901/

 

[SaintJude]

Actually it is B. But like MT Headed said, it's something you gotta memorize. I think HoltMD is trying to point out that there are actually 2 stages of arrests-one occurs in meiosis I and the other occurs in metaphase II.

Wiki is actually helpful here:
In females, meiosis occurs in cells known as oogonia (singular: oogonium). Each oogonium that initiates meiosis will divide twice to form a single oocyte and three polar bodies.[6] However, before these divisions occur, these cells stop at the diplotene stage of meiosis I and lie dormant within a protective shell of somatic cells called the follicle. Follicles begin growth at a steady pace in a process known as folliculogenesis, and a small number enter the menstrual cycle. Menstruated oocytes continue meiosis I and arrest at meiosis II until fertilization. .....
The metaphase II arrest is only broken by a Ca2+ rise initiated by the fertilizing sperm, so it will only move on to anaphase II if sperm is around.



So in summary for the MCAT:
So oocytes will arrest in prophase I of meiosis until puberty hits. Then once the menstrual cycle starts, oocytes will arrest in metaphase II until there is sperm around to indicate it should move on to complete meiosis II. Hope the summary helps.

 

[MedPR]

The answer is B until puberty. The logic? The same reason why Oxygen was named Oxygen and not Nitrogen. It just is.

 

[osprey099]

it is arrested in prophase 1 of meiosis. you just have to memorize it.

 

[CaptainScience]

The female primary oocyte is frozen at prophase 1 until puberty. Also, it's secondary oocyte is frozen at metaphase 2 until fertilization occurs.

 

[Temperature101]

Got it guys...I will have to memorize some of these stuff. I am suck at embryology...

 

[sniderwes]

I put "D" interface because it completes DNA replication before arresting...so I'm kind of pissed that B is the right answer since it arrests after interface and before meiosis I starts

 

[dyspareunia]

I put "D" interface because it completes DNA replication before arresting...so I'm kind of pissed that B is the right answer since it arrests after interface and before meiosis I starts

No it doesn't. Oocytes never replicate DNA.

 

[nihitmehta]

A. prophase of mitosis
B. prophase I of meiosis
C. prophase II of meiosis
D. interphase

You can cancel A out, Mitosis is of no use to a gamete since it's reductive division meiosis might be a better option. Cancel C out, if it's prophase 2 then the cell's are already halfway through meisosis, what's the logic to stop them at this step then? Finally, between interphase and meisosis Prophase 1. One way to think about this is as follows, Interphase consists of three phases right? G1 S and G2, From what I understand G2 is the phase where proteins are produced that will be required for division.


These cells are going to mature and go through meiosis eventually, translation of proteins takes a lot of ATP, kind of like an energy hump, what's the use of stopping before overcoming this energy expenditure? Why not spend the energy, when the bill for this ATP requirement is being footed for by the mother.


Finally, if it stops in Interphase ask yourself which phase, typically, G1 is the phase that cells can spend time in, but then these cells's would be like your stem cells. Stem cells in your ovaries don't make sense. They can't stay in the S phase, or G2 phase, because once you produce all the DNA, protein production, spend all that time and energy it's illogical to stop then. Better to have them getting started in meisosis, so all that needs to be done, is division and ready for use, division and use.

Anyway, to be honest with you it's kind of a gut thing, interphase doesn't sit right with me. I am sure someone can come up with a better reasoning then mine.

 

[dyspareunia]

A. prophase of mitosis
B. prophase I of meiosis
C. prophase II of meiosis
D. interphase

You can cancel A out, Mitosis is of no use to a gamete since it's reductive division meiosis might be a better option. Cancel C out, if it's prophase 2 then the cell's are already halfway through meisosis, what's the logic to stop them at this step then? Finally, between interphase and meisosis Prophase 1. One way to think about this is as follows, Interphase consists of three phases right? G1 S and G2, From what I understand G2 is the phase where proteins are produced that will be required for division.


These cells are going to mature and go through meiosis eventually, translation of proteins takes a lot of ATP, kind of like an energy hump, what's the use of stopping before overcoming this energy expenditure? Why not spend the energy, when the bill for this ATP requirement is being footed for by the mother.


Finally, if it stops in Interphase ask yourself which phase, typically, G1 is the phase that cells can spend time in, but then these cells's would be like your stem cells. Stem cells in your ovaries don't make sense. They can't stay in the S phase, or G2 phase, because once you produce all the DNA, protein production, spend all that time and energy it's illogical to stop then. Better to have them getting started in meisosis, so all that needs to be done, is division and ready for use, division and use.

Anyway, to be honest with you it's kind of a gut thing, interphase doesn't sit right with me. I am sure someone can come up with a better reasoning then mine.

Secondary oocytes stop in meiosis 2 (metaphase) so there's that. Protein synthesis all begins in G1 and continues through G2. There is a checkpoint at G2-M and many cells do arrest in G2.

Just remember that primary oocytes are in prophase 1 and don't complete meiosis 1 until ovulation. Then the secondary oocyte stays in metaphase 2 until it is fertilized.