Primary Spermatocyte = tetraploid or diploid?

[rocketbooster]

So I understand that primary spermatocytes are 4N, but First Aid as well as many books will list it as diploid (4N). What's the deal with not calling it tetraploid? If asked on Step 1, which do you go with?

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[JRjcu08]

So I understand that primary spermatocytes are 4N, but First Aid as well as many books will list it as diploid (4N). What's the deal with not calling it tetraploid? If asked on Step 1, which do you go with?

The "N" refers to a set of paired homologous chromosomes.

Spermatogonia are diploid because they have 46 sets of x-y chromosomes.
Primary spermatocytes are also diploid because they have replicated (mitosis) each x and each y to make 46 sets of x-x/y-y, so that in the first meiotic division they form 1 full gamete (23) of x-x, and 1 full gamete of y-y .

Tetraploid means there are four SETS of paired homologous chromosomes.

 

[rocketbooster]

The "N" refers to a set of paired homologous chromosomes.

Spermatogonia are diploid because they have 46 sets of x-y chromosomes.
Primary spermatocytes are also diploid because they have replicated (mitosis) each x and each y to make 46 sets of x-x/y-y, so that in the first meiotic division they form 1 full gamete (23) of x-x, and 1 full gamete of y-y .

Tetraploid means there are four SETS of paired homologous chromosomes.

So 4N = tetraploid, correct? Every book lists primary spermatocytes as "Diploid (4N)." Based on your definition, that would also be written as Diploid (tetraploid), lol. See...I'm still confused haha

Care to redefine N or ploidy? I think they just call it diploid still possibly because the 4N stage is only temporary and they define the ploidy based on pre+post division final stages? Or maybe they just consider it a "duplicated diploid?" Idk...

Oh and also your "gamete" definition is wrong. Gamete = sperm + egg/ovum. Your definition is actually the secondary spermatocyte/oocyte.

Anyone else care to define these? lol thanks!

 

[lrkoehle]

There are 4 chromatids (4N), but only one pair of each chromosome (diploid). Does that help? Probably not, because this is a somewhat confusing topic to explain without drawing something or doing an interpretive dance of some sort.

 

[withrye]

The monoploid number (X) is the number of chromosomes that make one complete set. For humans, this is 23. The haploid number (N) is the number of chromosomes in a gamete. For humans, this is also 23. The X number is what we refer to when we call cells in humans haploid, diploid, etc. A human somatic cell has two different complete copies of chromosomes, so we call it diploid (2X, 2N, 46 chromosomes total). A human gamete cell has one copy of chromosomes, so we call it haploid (X, N, 23 chromosomes total).

When we call a cell halpoid, we are saying how many unique copies of chromosomes it has. Imagine we take a halpoid cell with 23 unique chromosomes and triple all of those. We then have a cell that is (X, 3N, 69 chromosomes total), but still haploid.

When we call a cell diploid, it has 2 unique copies of each chromosome. When we double this, we get (2X, 4N, 96 chromosomes), and it's still called diploid. To call something tetraploid would be to say that 4X is present in the cell, or FOUR UNIQUE chromosomal sets.

 

[ctusfinest]

ploidy= sets of chromosomes, N= number of times gene is in the pool

therefor it is diploid because there are 2 chromosomes, but it is 4N because the gene is present four times.

haploid (1N) = l
haploid (2N)= X
diploid (2N) = ll
diploid (4N) = XX

Different books define N differently so this may not be consistent throughout everything you read, but I believe this is the way first aid defines the terms. If I'm wrong or this doesn't make sense please do tell.

 

[lemonade90]

With all the Ns in this thread, if the sperm did ever fertilize you'd be at risk for a choriocarcinoma.

 

[JRjcu08]

Sorry if my description wasn't good enough for you...
From Wiki: A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually. When mommy and daddy love each other very much...two of these come together and form an embryo. Sorry, that last part wasn't from wikipedia.

Also from wiki: Ploidy is the number of sets of chromosomes in a biological cell.
Ex) In a somatic cell, 46 chromosomes = 2n. 23 chromosomes , 2 copies of each chromosome (2). This means 1 N = 1 set of 23 chromosomes.

The # preceding N = # of strands of each chromosome. (sorry for getting it backwards before)
a strand = a chromatid
a chromosome ("sister chromatids") = 2 chromatids

Primary spermatocytes are not tetraploid because they are formed from a mitotic division. They still have the same number of chromoSOMES as the spermatogonia because replication of genetic material has occurred but the cell has not split- the number of chromosomes has not changed, the # of chromaTIDS has doubled --> replication in mitosis forms more chromaTIDS, not more chromosomes. If there is no cell division, ploidy cannot change -- they are "4"N because N for humans is 23, and each individual chromatid (each x, each y) increases the multiplier.

Spermatogonia have 1x, 1y for the sex chromosome = 1 X chromatid, 1 Y chromatid. The genetic material replicates but the cell does not split. Now there is one cell... 22 autosomes *2, 1 sex chromosome that is xxyy (4N- 4 chromatids for on the sex chromosome). The cell divides (equally, you hope) and you get two cells (secondary spermatocytes) that are 23N. 22 autosomes, 1 sex chromosome that is xx or yy.
Final spermatid = no change in the amount of genetic info, only splitting of the 2 previous cells giving 4 spermatids that each have 23 chromatids, 22 autosomal chromatids, 1 sex chromatid, which is an x or a y.

 

[rocketbooster]

Ahh, the last 2 posts help A LOT. Ploidy = unique chromosomes. A duplicated chromosome is still one unique chromosome. N = number of chromosomes in a gamete, which is 23 for humans. So, the secondary spermatocyte is haploid (2N), spermatid/sperm (gamete) is haploid (1N), etc.

Thanks for the clarification. Haha, I remember being confused about this way back in genetics in college. Back then, I only reached the level of understanding that the spermatogonia duplicated during the S phase before the first meiosis and that was enough to answer test questions haha. And in med school it came up again last year but I wasn't too overly concerned with the terminology since I understood the process and didn't want to waste time searching for the answer since I had plenty of other **** to study. Figured this would be the last time to actually find the answer since classes are now officially over forever. Thanks again.

 

[Kalyx]

Haploid is always written as "n," never as "2n," because the number before the "n" is the haploid number. The haploid number refers to the ***number of homologs per set of chromosomes***. Humans are diploid, so there are two homologs per unique set. Our ploidy number is 23, so there are 23 unique sets of chromosomes. "Tetraploid" would mean there were four homologs per set. Here's a good image showing that: http://www.google.com/imgres?imgurl...-9T9TeDembiQKYs9iCDg&ved=0CHcQ9QEwBg&dur=5659

After replication, there are technically four chromatids per unique chromosome set (2 homologs x 2 = 4) and this is what's known as the "tetrad." It is NOT tetraploid because tetraploid implies four distinct homologs per chromosome set. During meiosis 1, the homologous pairs separate, which is why the secondary spermatocytes are haploid. It seems that First Aid used the term "4N" to denote a tetrad, but that seems incorrect to me because convention would have it that "4N" would be tetraploid.

 

[DrDJShik]

my god this is the last time im going to read anything fact related on SDN...now I have to go re-learn this material so I can make sense of it again

 

[Azipropofol]

my god this is the last time im going to read anything fact related on SDN...now I have to go re-learn this material so I can make sense of it again

hahaa, you got me rollin dude.

 

[The kitchen sink]

my god this is the last time im going to read anything fact related on SDN...now I have to go re-learn this material so I can make sense of it again

Agreed. I am so lost now

 

[rocketbooster]

Haploid is always written as "n," never as "2n," because the number before the "n" is the haploid number. The haploid number refers to the ***number of homologs per set of chromosomes***. Humans are diploid, so there are two homologs per unique set. Our ploidy number is 23, so there are 23 unique sets of chromosomes. "Tetraploid" would mean there were four homologs per set. Here's a good image showing that: http://www.google.com/imgres?imgurl...-9T9TeDembiQKYs9iCDg&ved=0CHcQ9QEwBg&dur=5659

After replication, there are technically four chromatids per unique chromosome set (2 homologs x 2 = 4) and this is what's known as the "tetrad." It is NOT tetraploid because tetraploid implies four distinct homologs per chromosome set. During meiosis 1, the homologous pairs separate, which is why the secondary spermatocytes are haploid. It seems that First Aid used the term "4N" to denote a tetrad, but that seems incorrect to me because convention would have it that "4N" would be tetraploid.

Oh wow, you're right lol. I think it's safe to say everyone understands the mechanism of spermatogenesis, but the definitions are confusing. After doing some more google image and Wikipedia searching, I believe you are correct.

I think it comes down to this: First Aid used the wrong nomenclature. By convention, N= the number of unique chromosome sets. And yes, the primary spermatocyte is called a tetrad, not a tetraploid.

Spermatogenesis should be like this:

Spermatogonia - diploid, 2N, 46 single chromosomes
Primary spermatocyte - diploid, 2N, 46 sister chromatids (tetrad/bivalent)
Secondary spermatocyte - haploid, N, 23 sister chromatids
Spermatid - haploid, N, 23 single chromatids

Sister chromatid = 2 identical chromatids. In the primary + secondary spermatocytes, there are still only 2 and 1 unique sets of chromosomes so they are still diploid (2N) and haploid (N). HOWEVER, the centromere has a pair of sister chromatids bound to it. Th extra copy is not a unique set, but rather just a duplication/copy of the original so it's not counted as change in ploidy. Ploidy only changes when you go from primary to secondary spermatocytes, since you actually are halving the # of unique chromosome sets. The # of unique chromosome sets does not change in any other steps.

And, also, to be fair, I have seen other diagrams incorrectly use N just like First Aid. Thinking back to my old genetics class, though, N = number of unique chromosome sets. That's why I was confused with FA and made this post since FA was conflicting with my older knowledge haha.

 

[Kalyx]

Oh wow, you're right lol. I think it's safe to say everyone understands the mechanism of spermatogenesis, but the definitions are confusing. After doing some more google image and Wikipedia searching, I believe you are correct.

I think it comes down to this: First Aid used the wrong nomenclature. By convention, N= the number of unique chromosome sets. And yes, the primary spermatocyte is called a tetrad, not a tetraploid.

Spermatogenesis should be like this:

Spermatogonia - diploid, 2N, 46 single chromosomes
Primary spermatocyte - diploid, 2N, 46 sister chromatids (tetrad/bivalent)
Secondary spermatocyte - haploid, N, 23 sister chromatids
Spermatid - haploid, N, 23 single chromatids

Sister chromatid = 2 identical chromatids. In the primary + secondary spermatocytes, there are still only 2 and 1 unique sets of chromosomes so they are still diploid (2N) and haploid (N). HOWEVER, the centromere has a pair of sister chromatids bound to it. Th extra copy is not a unique set, but rather just a duplication/copy of the original so it's not counted as change in ploidy. Ploidy only changes when you go from primary to secondary spermatocytes, since you actually are halving the # of unique chromosome sets. The # of unique chromosome sets does not change in any other steps.

You've almost got it, just a couple of things to solidify. The **ploidy** number, the number of unique sets, does not change. It's the **haploid number**, a.k.a. "n", that changes in meiosis ("n/N" refers to the haploid number, not the ploidy number. You'll sometimes see this written as 2n = 23, which means that the haploid number is 2 and the ploidy number is 23).

In meiosis I, the ***homologous pairs separate***, giving you haploid daughter cells. They're haploid b/c the homologous pair for each chromosome is in the other daughter cell. In meiosis II, the ***sister chromatids separate*** (much like in mitosis).

If the ploidy number were to change in a meiotic division, you'd have a nondisjunction problem!

Hope that helps clarify things!

 

[polyboy112]

One tip that should help (though it may repeat what someone else has said -- too lazy to look): to determine ploidy count the number of centromeres.

For example, when you replicate the DNA prior to meiosis I, you double the DNA but there is no increase in centromere count. Therefore, it is 4n; but, you haven't actually increased the number of centromeres. Therefore, it is 4n and still diploid. After meiosis I, you have halved the number of centromeres (to 1) and thus it is 2n haploid. And, after meiosis II, you still have 1 centromere and thus it is n haploid.

 

[rocketbooster]

Yeah, I gotcha.

And here's another kicker: UWorld just said primary spermatocyte is 4N. FML

But yea, I get the concepts and understand how they are only diploid and haploid, not tetraploid. I think it should technically be "4n" like the above poster said, but different books use different upper/lowercase. Sigh.

So, if in the answer choices on Step 1 it asked you what are primary spermatocytes?
a) Diploid (4N)
b) Diploid (2N)
c, b, e garbage answers

Best to pick A, right? Even though it should probably say 4n...?

 

[Kalyx]

Hi there,

First of all, my apologies, I can't believe I did this but I mixed up "ploidy number" and "haploid number!" Out of all the details we went over it's those simple two that always have me confused. I actually did a quick check before posting, but the source was wrong, go figure.

Now I don't think I'll ever mix it up again: if we're talking about adding new homologs per unique set of chromosomes (i.e. chromosome 5), then we go from haploid--> diploid --> tetraploid, etc. All those words have "ploid" in them, so the "ploidy number" denotes the number of homologs per set. Humans have haploid gametes, diploid somatic cells.

My understanding is that 4n/N (I'm not sure there's a distinction between a small and upper-case "n"...) would be incorrect. Here's a helpful figure:

http://www.google.com/imgres?imgurl...6YhyK6IApacwKUI&sqi=2&ved=0CHcQ9QEwBA&dur=328

"4n" probably exists as an answer choice because some students will think of the replication that occurs before meiosis I, but this does not change the *ploidy number* (aha!) because it's not adding NEW homologs, rather replicating the ones that exist. The total number of chromatids/pieces of chromosome will double, but again, this does not change the ploidy number because we're not adding new homologs (like in fertilization) nor are we adding new unique sets of chromosomes (like in a nondisjunction), which would change the **haploid number**.

Again, my apologies for my error above! I think if you look in some textbooks, you'll see that the primary spermatocytes are labelled "2n."