Quick Bio Question

[kov82]

---

Members don't see this ad.

Is an ootid in human females always a zygote? since an unfertilized egg is released by the ovaries as a secondary oocyte? and if the egg is not fertilized, its released as a secondary oocyte during menstruation right? so an ootid is always a zygote? but in my book, the ootid develops from the secondary oocyte, but the book says the ootid is haploid, and I know the zygote is diploid, so an ootid does not exist in humans?


just out of curiosity: birth control pills contain synthetic hormones resembling estrogen and progesterone, making the females body think she is pregnant, which prevents the ovarian cycle (but not the uterine cycle) by exerting negative feedback control on the hypothalamus and pituitary, does this mean ovulation does not occur? (I'm guessing thats the whole point of the pill)
so my main question is: does a woman that takes birth control for a long period of time have more primary oocytes than she "should" have (without ever having taken the pill)? or do the ovaries "get rid" of, or degenerate the 6-12 primary oocytes some how each month even though she is on the pill?

 

[Ryltar]

The ootid is haploid because it is not fertilized yet. Meiosis produces haploid cells from diploid cells, thus there is a reduction in ploidy (2N->1N). Upon fertilization, the 1N genetic material of the sperm combines with the 1N genetic material of the egg to produce a 2N zygote.

Birth control pills mimic progesterone primarily, and they bind to the progesterone receptors in the endometrium; however, they don't have the same effect as progesterone. Thus, they essentially compete with progesterone for the receptors, reducing the effective concentration of progesterone. With low effective concentration of progesterone, the thickening of the endometrium cannot be maintained, thus preventing implantation of the blastocyst. The oocyte is still lost in menstruation.

She would have the same amount of oocytes. Women have a certain number of oocytes at birth and that doesn't change until ovulation occurs, with decrease in egg count by one or more each ovulation (multiple ovulation can occur).

 

[Ryltar]

Meiosis produces four ootids. Cytoplasm from three of the four ootids is concentrated in one ootid, and the other 3 ootids form polar bodies (cytoplasmless ootids), which disintegrate. The secondary oocyte oocyte is released during menstruation along with part of the endometrium wall.

Thus, not all of the ootids become the egg that gets fertilized. An ootid, can either become a secondary oocyte or a polar body.

 

[kov82]

I know about the fertilized egg being diploid 2n, and that the ootid is haploid 1n, my question is about the order of events within a human female, do they include the developmental stage of "ootid"? because the eggs in ovaries, are all in the primary oocyte stage until 6-12 begin developing further into secondary oocytes during the ovarian cycle, out of those 6-12, only one secondary oocyte (sometimes more) remains and during ovulation, that secondary oocyte is released into the oviduct, where, after copulation, a sperm fertilizes the secondary oocyte in the upper regions of the fallopian tube, so then its a zygote 2n, my question is: what happened to the "ootid"? or does it NOT exist in human females?
Ryltar: I wrote the above message before I saw your second message

but in regards to that second message: I've read that the secondary oocyte 👎, goes through a second meiotic division to give the ootid 👎 and the second polar body from the secondary oocyte degenerates, the ootid then goes through further development and differentiation to give the ovum, are you sure that the ootid can become a secondary oocyte?

 

[Ryltar]

I believe ootid is another term for one of the four daughter cells produced by meiosis, just like spermatid refers to one of the four spermatids produced by meiosis in males. I think you mean age 6-12? I know they remain primary oocytes until puberty, then they become secondary oocytes. One of the four ootids becomes the primary oocyte, then becomes the secondary oocyte, and then is fertilized by sperm to become the zygote.

 

[Ryltar]

Cliffs AP Biology gives a really good explanation of this topic.

 

[kov82]

from what I read spermatogenisis and oogenisis, are very similar in terms of stages, a male germ cell (2n) develops goes through mitosis to give a spermatogonium (2n), that develops further to give a primary spermatocyte (2n), the primary spermatocyte goes through a meitoic division to give two secondary spermatocyes 👎 (that remain in cytoplasmic contact throughout their development), the two secondary spermatocytes go through a second meiotic division to give four spermatids 👎 that differentiate and mature into sperm cells 👎,

in oogenesis
a female germ cell (2n) goes through mitosis to give an oogonium (2n), that further develops into a primary oocyte (2n), which goes through meiosis to give a secondary oocyte, the two daughter cells of that meiotic division (unlike in males) have a very large difference in cytoplasmic division, the smaller daughter cell is called the polar body, the larger one is the secondary oocyte 👎, after a second meiotic division you have the ootid along with a second polar body (I screwed up in an earlier message saying that the second polar body was attached to the secondary oocyte), the second polar body is 3 daughter cells attached to the one big ootid 👎 which further develops into the ovum and the polar bodies degrade. That is what is in my book.
The book also states that the eggs are "frozen" in the ovaries, as primary oocytes, what I was referring to by 6-12 is that during the ovarian cycle, its not one or two but anywhere between 6-12 of the pirmary oocytes (out of many thousands) that begin to develop into secondary oocytes surrounded by follicle cells, out of those 6-12 primary oocytes, usually one (but sometimes two, giving fraternal twins) secondary oocyte is released into the fallopian tube, the rest of them degrade, so the egg is released as a secondary oocyte 👎 during ovulation, and is fertilized into a zygote by a sperm, according to the events of oogenesis in my book, either the ootid does not exist in humans, OR the zygote can be referred to as an ootid, or my book is wrong?

 

[kov82]

repost

 

[kov82]

I just looked through my ap cliffs bio book the 3rd edition, it actually doesn't mention ootids on page 212.
One thing to remember though is that after puberty menstruation starts, the eggs themselves are all still in the primary oocyte phase, further development into secondary oocytes only happens for about 6-12 of the primary oocytes each month, and out of those 6-12 only one is usually released during ovulation.

 

[Ryltar]

What you stated in the above message is dead on. The ootid does exist in humans just as the spermatid exists in humans. I looked up the precise definition of ootid, which is,"the nearly mature ovum after penetration by the spermatozoon and completion of the second meiotic division but before the fusion of the pronuclei to form the zygote."

Disregard that four ootids are formed by meiosis. Only one is formed. So to clarify things, the mere penetration of the sperm is what initiates meiosis II of the egg. This results in one ootid, which becomes the zygote upon fusion of pronuclei.

 

[Ryltar]

So to sum things up:

Secondary oocyte -> penetration by sperm -> Meiosis II, release of 2nd polar body -> ootid -> fusion of pronuclei -> zygote

 

[kov82]

wow so its right in between secondary oocyte and a zygote, my book didn't mention that, thanks a lot.