AQA A-Level Meosis Division, Spermatogenesis

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User148
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Hi,

I'm quite confused right now.

9a: https://pmt.physicsandmathstutor.com...ll%20Cycle.pdf

The gametes produced are 30 and 31. I have assumed that the cell replicates its DNA to give 120 chromosomes in total (4n = 120). Then I assumed it divided twice to give 30 (2n = 60, n = 30).

So I thought the same logic would apply here in question 1a: https://pmt.physicsandmathstutor.com...0Variation.pdf

The mark scheme says 46 TO 23, 23 TO 23, 23, 23, 23.

I tried to apply the same logic as the previous question and do 46 x 2 = 92 (4n = 92). 2n = 46 and n = 23. That didn't work though.

If the sperm cell started out as 23, it would replicate to form 46. Then that would have to divide twice (4n to 2n to n), but that isn't possible as it would give 11.5.

I'm really stuck on this and would appreciate your help!
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hafsah002
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(Original post by User148)
Hi,

I'm quite confused right now.

9a: https://pmt.physicsandmathstutor.com...ll%20Cycle.pdf

The gametes produced are 30 and 31. I have assumed that the cell replicates its DNA to give 120 chromosomes in total (4n = 120). Then I assumed it divided twice to give 30 (2n = 60, n = 30).

So I thought the same logic would apply here in question 1a: https://pmt.physicsandmathstutor.com...0Variation.pdf

The mark scheme says 46 TO 23, 23 TO 23, 23, 23, 23.

I tried to apply the same logic as the previous question and do 46 x 2 = 92 (4n = 92). 2n = 46 and n = 23. That didn't work though.

If the sperm cell started out as 23, it would replicate to form 46. Then that would have to divide twice (4n to 2n to n), but that isn't possible as it would give 11.5.

I'm really stuck on this and would appreciate your help!
the answer 46 TO 23, 23 TO 23,23,23,23 is correct because the same logic can't be applied both times because one speaks of mitosis and the other of meiosis.

In mitosis the mother cell divides to form 2 diploid cells which is where u apply the 4n to 2n to n logic.

In gametogenesis (keep in mind that this doesn't refer to the fusing of 2 gametes to give a diploid cell) the germinal epithelial cells start with 43 (diploid) cells [not 23 as you had suggested] and divide via meiosis 1 into 2 cells of 23 (haploid) which then undergo meiosis 2 to gives 4 haploid cells.

I don't think its making much sense but it's the best i can do x
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User148
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(Original post by hafsah002)
the answer 46 TO 23, 23 TO 23,23,23,23 is correct because the same logic can't be applied both times because one speaks of mitosis and the other of meiosis.

In mitosis the mother cell divides to form 2 diploid cells which is where u apply the 4n to 2n to n logic.

In gametogenesis (keep in mind that this doesn't refer to the fusing of 2 gametes to give a diploid cell) the germinal epithelial cells start with 43 (diploid) cells [not 23 as you had suggested] and divide via meiosis 1 into 2 cells of 23 (haploid) which then undergo meiosis 2 to gives 4 haploid cells.

I don't think its making much sense but it's the best i can do x
Hi! Thanks for your reply!

Question 9 in the first link shows an arrow which is labelled with 'meiosis'. When you say mitosis, do you mean the first division of meoisis?
Also wouldn't mitosis just be 4n to 2n as it is one division then meiosis is 4n to 2n to n as it is two divisions?
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