(Solved) Gamete Formation Definition?

jellyksong

wrote...

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13 years ago

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 Rightwards Arrow

(mitosis) 2 primary spermatocytes
2 primary spermatocytes Rightwards Arrow

(meiosis I) 4 secondary spermatocytes
4 secondary spermatocytes Rightwards Arrow

(meiosis II) 8 spermatids
development.... Rightwards Arrow

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?

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duddy

wrote...

Staff Member

13 years ago

Sure, I will try to explain it with this diagram:

https://courses.stu.qmul.ac.uk/smd/kb/microanatomy/humandev/images/Spermatogenesis.jpg

You start off with a spermatogonium, which undergoes meiosis. Meiosis I is technically the same as mitosis, with the exception of crossing over, which doesn't take place in mitosis. So after cytokinesis (the splitting of the cells), it undergoes meiosis II, where the two daughter cells, each containing 46 chromosomes, splits into half. 46 becomes two 23-chromosomed cells and the other 46-chromosomed cell becomes two 23-chromosomed cells... this equals a total of 4 cells containing 23 chromosomes. These are called spermatids which go on to mature into sperm cells.

Make sense jellyksong?

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jellyksong Author

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13 years ago Edited: 13 years ago, jellyksong

From my understanding, the spermatogonium undergoes mitosis, not meiosis. The daughter cell from spermatogonium is called the primary spermatocyte, which then undergoes meiosis.

My problem is in the diagram you provided.. The left side of the diagram shows the cell dividing and ultimately becoming sperm cells, but if you look at the beginning of it, it shows the spermatogonium mitotically dividing to become only one daughter cell, which makes no sense.

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jellyksong Author

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13 years ago

Actually, the diagram has an arrow pointing backwards towards the spermatogonium, doesn't it?

So...does this mean that the spermatogonium undergoes mitosis to form one primary spermatocyte, and one spermatogonium (which doesn't undergo meiosis until some future point in time)?

If that's the case it's still somewhat inconsistent...

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star

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13 years ago

Quote from: jellyksong (13 years ago)

The spermatogonium undergoes mitosis, not meiosis. The daughter cell from spermatogonium is called the primary spermatocyte, which then undergoes meiosis

That is correct, c'mon Duddy, you know better than that Face with Stuck-out Tongue

You're a guy!

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duddy

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Staff Member

13 years ago

Sorry jellyksong, and star, be quiet Slight Smile

A spermatogonium cell divides by mitosis to produce two diploid cells. One of these two cells then undergoes meiotic division to produce four haploid cells that will become sperm while the other remains as a spermatogonium. In that way, the male never runs out of spermatogonia to produce sperm. Adult males produce an average of 100–200 million sperm each day and can continue to do so throughout most of the rest of their lives.

The diploid daughter cell that begins meiosis is called a primary spermatocyte. In humans it has 23 pairs of homologous chromosomes (46 chromosomes total), and each chromosome is duplicated, with two chromatids. The first meiotic division separates the homologous chromosome pairs, producing two haploid secondary spermatocytes. However, each chromosome still consists of two duplicate chromatids.

Each of these cells then undergoes the second meiotic division to separate the chromatids and produce two haploid cells, the spermatids. Therefore, a total of four haploid spermatids are produced from each primary spermatocyte. All of these cells constitute the germinal epithelium of the seminiferous tubules because they “germinate” the gametes.

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duddy

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Staff Member

13 years ago

Tell me if that makes more sense Undecided

Smiling Face with Open Mouth and Tightly-closed Eyes

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jellyksong Author

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13 years ago

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Gamete Formation Definition?

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