Gamete Formation Definition? - (Apr/22/2011 )

In gamete formation, it's defined as (let's say spermatogenesis) "one spermatogonium cell forms a total of 4 sperm".
However, also following the definition of spermatogenesis:
spermatogonium -->(mitosis) 2 primary spermatocytes
2 primary spermatocytes -->(meiosis I) 4 secondary spermatocytes
4 secondary spermatocytes --> (meiosis II) 8 spermatids
development.... --> 8 sperm

I'm confused at this inconsistency. Technically, if one spermatogonium undergoes mitosis to form 2 primary spermatocytes, then the definition should actually be "one primary spermatocyte forms a total 4 sperm".

The diagrams in my Barron's AP book show a spermatogonium undergoing mitosis to form only ONE (as opposed to two) primary spermatocytes, which makes no sense, but does give 4 sperm as the result.

Anyone care to explain this to me?

I think they mean: "In spermatogenesis, four sperm cells are produced as a result of one cell (spermatogonium) undergoing meiosis"

or like you said: from 1 primary spermatocyte.

I dont know about the book, but maybe its like this:

This diagram actually makes more sense, since the spermatogonium divides into two cells: a spermatogonium (that doesn't undergo meiosis until some point in the future?) and a primary spermatocyte (which does undergo meiosis I suppose).

However, isn't the "additional spermatogonia" and the "primary spermatocyte" in this diagram 100% genetically identical? There should be no difference between them, so there's really no point in differentiating them. I would expect that in vivo, the spermatogonium does actually divide into two primary spermatocytes that both undergo meiosis...is it just some technicality on the definition's side?

It's just confusing because a lot of the sources I checked contradict each other...no one really explains it fully.

By definition, a spermatogonium produces 4 sperm, but by technicality it produces 8?

Kenny Song on Sat Apr 23 01:27:56 2011 said:

Eh, not quite sure, but I can tell you there are 3 types of spermatogonium. Maybe this will make it clearer:


The Ad spermatocytes (diploid) continue replicating asymmetrically to form one progenitor cell and one daughter (son?) cell. This is the perpetual source of progenitor cells.

The diploid Ap daughter cell commits to a course of differentiation that continues through successive, symmetric divisions. Each round of division gives a different recombination in the final haploid. The diploid Ap will divide mitotically to form 2 Bs, which then become 4 primaries, and 8 secondaries. The secondaries then divide to form the haploid spermatids.

From my reckoning, you have 1B-->2 diploid primaries-->4 diploid secondaries-->8 haploid spermatids.

I think you are missing some basic knowledge or misunderstanding something.

Its pretty simple in the end:


You have a bunch of Ad cells (spermatogonia) that undergo mitosis ... thats all they do. And they either form new Ad cells that stay in this "pool" and keep dividing or they form a type Ap cell.. Now this Ap cell leaves this "pool" to undergo a series of mitotic divisions untill they form type B cells and these cells undergo one more mitotic division to form primary spermatocytes. And thise cells ondergo two meiotic divisions to form spermatides in the end.
(4 spermatids for each primary spermatocyte).


So all together: Ad cells, they simply divide to form new cells (they keep the population of cells in order) and at some point a few of these cells form Ap cells in stead of Ad cells.. Those Ap cells leave the pool of Ad cells to start their journey to become spermatides.

So spermatogonia either stay as Ad cells to keep the population of cells in order or they become Ap type spermatogona to make spermatides...

I hope you get the idea now? In fact its just one big collection of cells that divide the entire time and either they form a Ap cell or Ad cell....

Kenny Song on Sat Apr 23 01:27:56 2011 said:

==> that primary spermatocyte that starts meiotic division comes from type Ap , that aditional cell is indeed also a type Ap cell and will also undergo some mitotic divisiosn to form such a primary cell.. SO yes, they are the same.
In fact: the shedule shows only halve of what happens: you need to double it... You have indeed two primary cells ...
(this is just an example on how 1 Ad cells becomes 2 Ap cells by mitotic divion... so those two cells "leave the pool" of Ad cells.)


Off course: the figure could also just mean (or wants to state) that beside forming a type Ap cell, you can also form Ad cells that keep dividing.. This is just a figure to show what happens , how spermatides are formed. The part in where you have Ad cells just dividing by mitotic division is often not showed because its not that intersting to show, because the only thing that happens is that they divide...


I hope this made it clear?