VCAA 07 question

[JV-12]

Question 4 (multiple choice)
The edible pea (pisum sativum) has a diploid number of 14. Specific cells in the ovary undergo meiosis to produce gametes.
The number of DNA molecules in one of these cells at the beginning of meiosis would be
A. 7
B. 14
C. 21
D. 28

Can anyone explain to me this question? The answer stated is option D, which confuses me. I initially chose option B because If the diploid number is 14, it means there are 14 chromosomes, and doesn't one chromosome= one molecule of dna?

[hellovee]

The question states BEGINNING OF MEIOSIS, this means DNA replication has already taken place.
Therefore the chromosomes will replicate into sister-chromatids.
So 14 times 2 = 28. The answer is D

 

[saheh]

Oooo yeah devil question
I probably would've chose 14 too, but after closer thinking:

It's because DNA replicates at the start of meiosis,

So your 14 chromosomes become double armed structures, where each arm/chromatid is a DNA molecule
Therefore 28

Which will halve to 14 in first meiosis division,
And then 7 in the second

[JV-12]

so in the beginning of meiosis the chromosomes are single stranded? and one chromatid equals one molecule of DNA?

[saheh]

Not exactly....well before meiosis the chromosomes are just chilling around, all unwound and relaxed
And then they coil up, and replicate and become double armed,
This is all in the S phase of your cell cycle,  (remeber g, s, g  is growth and synthesis and then p m a t  is your mitosis/meiosis)
Then when meiosis begins they have already become double armed structures, each a molecule of DNA joined at the centromere,
Therefore at the beginning of meiosis there's 28, already double armed

[JV-12]

okay thanks heaps! i get it now (:

[saheh]

Yeah!? Awesome good luck tomorrow!!

[itsdanny]

One question. It discusses about the specific cells in the ovary undergo meiosis to produce gametes, which are called the germ line cells; to produce gametes. Would you say germ cells are diploid or haploid? Since germ cells undergo Meiosis to produce gametes, would that imply they're haploid?

Wait. I'm having a brain fart at the moment. So, prior to Meiosis I, how many chromosomes are present in the cell (in relations to a normal human)? That amount will then double in the S Phase, and will go through reductional division, halving the amount of chromosomes present in the initial cell which has cleaved to form each of the two haploid cells. It then goes through another round of division, this time, reducing the amount of chromatids (not chromosomes really right?) by half, and you end up with haploid cells with 23 chromosomes, each consisting of one chromatid. Could someone correct any mistakes or errors I've just written? That'd be great thanks!

[saheh]

One question. It discusses about the specific cells in the ovary undergo meiosis to produce gametes, which are called the germ line cells; to produce gametes. Would you say germ cells are diploid or haploid? Since germ cells undergo Meiosis to produce gametes, would that imply they're haploid?

Wait. I'm having a brain fart at the moment. So, prior to Meiosis I, how many chromosomes are present in the cell (in relations to a normal human)? That amount will then double in the S Phase, and will go through reductional division, halving the amount of chromosomes present in the initial cell which has cleaved to form each of the two haploid cells. It then goes through another round of division, this time, reducing the amount of chromatids (not chromosomes really right?) by half, and you end up with haploid cells with 23 chromosomes, each consisting of one chromatid. Could someone correct any mistakes or errors I've just written? That'd be great thanks!

1.) yeah I reckon that inference could be made? Seems logical...

2.) all right except S phase occurrsbefore meiosis begins. So when meiosis begins there are 46x2 so 92 DNA molecules(? I can't count it seems right) (in the form of 46 chromosomes of double armed structure)

Then meiosis I, the 46 paired, double armed homologous chromosomes separate so each resulting cell has 23 chromosomes, comprised of two chromatids.
Then meiosis II, chromatids split, each cell has 23 chromatids.
Voila

[itsdanny]

One question. It discusses about the specific cells in the ovary undergo meiosis to produce gametes, which are called the germ line cells; to produce gametes. Would you say germ cells are diploid or haploid? Since germ cells undergo Meiosis to produce gametes, would that imply they're haploid?

Wait. I'm having a brain fart at the moment. So, prior to Meiosis I, how many chromosomes are present in the cell (in relations to a normal human)? That amount will then double in the S Phase, and will go through reductional division, halving the amount of chromosomes present in the initial cell which has cleaved to form each of the two haploid cells. It then goes through another round of division, this time, reducing the amount of chromatids (not chromosomes really right?) by half, and you end up with haploid cells with 23 chromosomes, each consisting of one chromatid. Could someone correct any mistakes or errors I've just written? That'd be great thanks!

1.) yeah I reckon that inference could be made? Seems logical...

2.) all right except S phase occurrsbefore meiosis begins. So when meiosis begins there are 46x2 so 92 DNA molecules(? I can't count it seems right) (in the form of 46 chromosomes of double armed structure)

Then meiosis I, the 46 paired, double armed homologous chromosomes separate so each resulting cell has 23 chromosomes, comprised of two chromatids.
Then meiosis II, chromatids split, each cell has 23 chromatids.
Voila

Okay, so are you saying before S phase, there are 23 pairs of chromosomes present (thus 46 individual chromosomes consisting of one chromatid)? Thus if this is the inference that I have received, then germ line cells must be diploid, not haploid. And yes, I'm not sure where I made the inference that S phase is after Meiosis, but I hope I don't mislead the examiners with that. But thanks everything else is clear

[saheh]

Yep I'm guessing that's right... (Because then they replicate in  s phase)

And yeah all good...I don't reckon they'd asking a question requiring thaaaaat much detail...maybe though? Prob mc
Good luck!!

[itsdanny]

Yep I'm guessing that's right... (Because then they replicate in  s phase)

And yeah all good...I don't reckon they'd asking a question requiring thaaaaat much detail...maybe though? Prob mc
Good luck!!

Thank you, you too.
I was really confused with the above, but it seems pretty clear that. I originally thought that the starting cells (referring to interphase here) of Meiosis and Mitosis were different, in that they both contained a different number of chromosomes than to each other? Although, from this, they both start with an initial 46 chromosomes (or 23 pairs), so that was nice, thanks.

[saheh]

Yep! So that got me thinking
This is right yeah?  :

Both start with 46
Mitosis
-they are replicated too...so 92 dna again
-however they create one line at cell equator
-chromatids seperate and so 46 in each cell

Meiosis
-92 DNA strands
-however homologous chromosomes pair up and then they do the splits
And so on

[itsdanny]

Yes, that's what I believe to be correct as well. Any further input from anyone else to verify and confirm this would be of great gratitude as well, thank you.

[saheh]

Sweet! We got this!
Good luck tomorrow!!!!!!!! We'll rock it!