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Help with cell division question

Hi guys, hope you're cool.
Can anyone help me with this question as I don't understand it and the mark scheme isn't clear for me?
For the first question I drew
- one long white one and one short black one
- one long black one and one short white one
- 2 short black and white ones
- 2 long black and white ones
Is this correct?
And for part ii of the second question why is it not 4 for the second question because doesn't mitosis produce genetically identical cells so wouldn't it be 8 chromosomes across 2 nuclei or have 2 immature pollen grains fused together to make this?
Thanks
Original post by 11plusboy
Hi guys, hope you're cool.
Can anyone help me with this question as I don't understand it and the mark scheme isn't clear for me?
For the first question I drew
- one long white one and one short black one
- one long black one and one short white one
- 2 short black and white ones
- 2 long black and white ones
Is this correct?
And for part ii of the second question why is it not 4 for the second question because doesn't mitosis produce genetically identical cells so wouldn't it be 8 chromosomes across 2 nuclei or have 2 immature pollen grains fused together to make this?
Thanks

Hi,

For the first question, your first two responses seem correct to me. However I couldn't understand the last two.
Meiosis is a reduction division, which means it reduces the original chromosome number to half (46 to 23 in each).

The diploid cell initially had 4 chromsomes (2 pairs of homologous chromosomes). Notice that the long black and long white are one pair of homologous chromosome, and the short black and short white are another pair of homologous chromosomes.
A cell, after meisosis, receives either one of the chromosomes from the homologous pair.

So the 4 possible chromosomes are:
- one long white one and one short black one
- one long black one and one short white one
- one long white one and one short black one
- one long black one and one short white one

So there are only 2 possibilities.

For the second question, mitosis produces genetically identical cells, as you said. That is another way of saying the chromsome number is mantained. So if the single nucleus immature pollen grain has 8 chromosomes, then after mitosis, BOTH the nuclei will have 8 chromsomes.

The 8 chromosomes aren't divided 'across' the nuclei. During mitosis, the chromosomes duplicate so that 8 becomes 16. Then they are divided across the nuclei so that EACH has 8.

Hope this is clear and not confusing
20200514_075705.jpg

Remember chromosomes line-up during independent assortment irrespective of their maternal and paternal origin.

So depending on how they line up during independent assortment, there IS 4 options. I've attached a picture showing the possible combination pathways.

Agree with @qwert7890 explanation for the second part, 8 for both.
(edited 3 years ago)
Reply 3
Original post by HarisMalik98
20200514_075705.jpg

Remember chromosomes line-up during independent assortment irrespective of their maternal and paternal origin.

So depending on how they line up during independent assortment, there IS 4 options. I've attached a picture showing the possible combination pathways.

Agree with @qwert7890 explanation for the second part, 8 for both.

Ah okay so this is because the long white one and the long black one are a homologous pair of chromosomes and the two short ones are homologous as well?
I thought for some reason that the two black ones were homologous and the two white ones were homologous
Original post by 11plusboy
Ah okay so this is because the long white one and the long black one are a homologous pair of chromosomes and the two short ones are homologous as well?
I thought for some reason that the two black ones were homologous and the two white ones were homologous

Yes.

Homologous chromosomes are chromosomes with the same genes at each corresponding loci. So they are the same size.
Original post by HarisMalik98
20200514_075705.jpg

Remember chromosomes line-up during independent assortment irrespective of their maternal and paternal origin.

So depending on how they line up during independent assortment, there IS 4 options. I've attached a picture showing the possible combination pathways.

Agree with @qwert7890 explanation for the second part, 8 for both.

Hi,

I agree with you, but I believe your diagram is slightly misleading. Meiosis 1 results in 2 cells (ex. A and B)

Now independent assortment tells us that the 2 cells that are produced (A and B) can have 4 possible combinations as you have highlighted. Just don’t want any confusion here.
Original post by qwert7890
Hi,

I agree with you, but I believe your diagram is slightly misleading. Meiosis 1 results in 2 cells (ex. A and B)

Now independent assortment tells us that the 2 cells that are produced (A and B) can have 4 possible combinations as you have highlighted. Just don’t want any confusion here.


Yes, of course.

In the post I said the diagram was showing the possible combinations. It is not indicative of the actual process

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