# Biology

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Thread starter 5 years ago
#1
This question is in my as biology edexcel book biology b that is. The question says "a diploid cell has 20 pairs of homologous chromosomes. How many will be present in a cell produced from this cell by: a)Mitosis b)Meiosis"
Now the answer for the mitosis is 20 chromosomes for mitosis and 10 for meiosis but I can tell that it does not seem right at all. As 20 pairs of chromosomes means 40 chromosomes and at the end of mitosis it will have 40 chromosomes the same number and at the end of meiosis it will have half of the 40 so 20. Some clarity would be useful on this matter. Thanks in advance
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5 years ago
#2
(Original post by RetakeStudent07)
This question is in my as biology edexcel book biology b that is. The question says "a diploid cell has 20 pairs of homologous chromosomes. How many will be present in a cell produced from this cell by: a)Mitosis b)Meiosis"
Now the answer for the mitosis is 20 chromosomes for mitosis and 10 for meiosis but I can tell that it does not seem right at all. As 20 pairs of chromosomes means 40 chromosomes and at the end of mitosis it will have 40 chromosomes the same number and at the end of meiosis it will have half of the 40 so 20. Some clarity would be useful on this matter. Thanks in advance
It is asking for the amount of chromosomes in one cell produced from mitosis and meiosis. You're right in thinking the number of chromosomes double in mitosis, but after cytokinesis, the number of chromosomes in each cell halves. Mitosis produces cells identical to the parent cell, so the number of chromosomes in each cell produced will be the same as the parent cell, which in this case is 20.

For meiosis, just like in mitosis, the cell undergoes DNA replication which doubles the amount of chromosomes. You're correct in thinking a gamete (produced by meiosis) has half the number of chromosomes that a cell produced by mitosis has, but remember that mitosis produces identical daughter cells to the parent cells, which means meiosis produces cells with half the number of chromosomes as the parent cell (before it has undergone DNA replication). Meiosis undergoes two cycles of 'cytokinesis'.

Here's what happens (simplified):
Mitosis:
Diploid cell: 20 chromosomes
DNA replication: 40 chromosomes
Cytokinesis: separates the sister chromatids into 2 identical daughter cells, so chromosome number is 20 again.

Meiosis:
Diploid cell: 20 chromosomes
DNA replication: 40 chromosomes
Cell division: 20 chromosomes, 2 cells.
Cytokinesis (meiosis 2): 10 chromosomes, 4 (haploid) cells.
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Thread starter 5 years ago
#3
(Original post by Amefish)
It is asking for the amount of chromosomes in one cell produced from mitosis and meiosis. You're right in thinking the number of chromosomes double in mitosis, but after cytokinesis, the number of chromosomes in each cell halves. Mitosis produces cells identical to the parent cell, so the number of chromosomes in each cell produced will be the same as the parent cell, which in this case is 20.

For meiosis, just like in mitosis, the cell undergoes DNA replication which doubles the amount of chromosomes. You're correct in thinking a gamete (produced by meiosis) has half the number of chromosomes that a cell produced by mitosis has, but remember that mitosis produces identical daughter cells to the parent cells, which means meiosis produces cells with half the number of chromosomes as the parent cell (before it has undergone DNA replication). Meiosis undergoes two cycles of 'cytokinesis'.

Here's what happens (simplified):
Mitosis:
Diploid cell: 20 chromosomes
DNA replication: 40 chromosomes
Cytokinesis: separates the sister chromatids into 2 identical daughter cells, so chromosome number is 20 again.

Meiosis:
Diploid cell: 20 chromosomes
DNA replication: 40 chromosomes
Cell division: 20 chromosomes, 2 cells.
Cytokinesis (meiosis 2): 10 chromosomes, 4 (haploid) cells.
I understand that. But no where does the question make it clear that this is after interphase. If a cell has 20 homologous chromosomes would it not have 40 in total and after mitosis the same 40?
0
5 years ago
#4
(Original post by RetakeStudent07)
I understand that. But no where does the question make it clear that this is after interphase. If a cell has 20 homologous chromosomes would it not have 40 in total and after mitosis the same 40?
How many will be present in a cell produced from this cell.

Mitosis is not DNA replication. It is the process of prophase, metaphase, anaphase and telophase. Mitosis is basically the process of cells dividing. Therefore, any cell produced from this cell by mitosis will be a daughter cell identical to the parent cell.

If the question said "how many will be present in the cell after interphase?" then the answer would be 40. But because it's asking for the chromosomes in cells produced by mitosis, it means after cell division has taken place
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Thread starter 5 years ago
#5
(Original post by Amefish)
How many will be present in a cell produced from this cell.

Mitosis is not DNA replication. It is the process of prophase, metaphase, anaphase and telophase. Mitosis is basically the process of cells dividing. Therefore, any cell produced from this cell by mitosis will be a daughter cell identical to the parent cell.

If the question said "how many will be present in the cell after interphase?" then the answer would be 40. But because it's asking for the chromosomes in cells produced by mitosis, it means after cell division has taken place
Thank you. It makes sense. Sometimes the questions they ask are too vague
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