a level biology mitosis question

In interphase, the trout body cell has 80 chromosomes (according to the question.

In prophase, they also have 80 chromosomes, even though the mass of DNA has been doubled, because each chromosome now has double the DNA.

The number of chromosomes will be 80 in telophase as each of the 2 nuclei have 80 chromosomes, but each of them now have the normal amount of DNA.

Egg cells are haploid so they have 40 chromosomes.

The body cell in prophase has a mass of DNA of 50 as the amount of DNA has doubled from 25 (the normal amount).

Each egg cell has half the DNA (because half the chromosomes) so 12.5 mass of DNA.

Check the answer?

Reply 2

Biolover2020

OP

11

Original post by Abedshehabi

In interphase, the trout body cell has 80 chromosomes (according to the question.

In prophase, they also have 80 chromosomes, even though the mass of DNA has been doubled, because each chromosome now has double the DNA.

The number of chromosomes will be 80 in telophase as each of the 2 nuclei have 80 chromosomes, but each of them now have the normal amount of DNA.

Egg cells are haploid so they have 40 chromosomes.

The body cell in prophase has a mass of DNA of 50 as the amount of DNA has doubled from 25 (the normal amount).

Each egg cell has half the DNA (because half the chromosomes) so 12.5 mass of DNA.

Check the answer?

ok thanks! where im getting confused is that i thought a chromatid is half of a chromosome, so does the definition of a chromosome change during mitosis?

Reply 3

Sorry for the late response.

A chromatid is half of a CONDENSED chromosome.

In the human body (for example), a normal cell (not in mitosis) has 23 pairs of chromsomes, which are unwound in the form of chromatin and associated with histones.

In the S phase of interphase, the amount of DNA doubles. During prophase, the chromosomes condense, each having 2 sister chromatids. Each chromatid has an exact DNA copy of the original chromosome. This means each chromosome has double the amount of DNA. However, we still say there are 23 pairs of chromsomes.

Refer to my beautiful MS paint diagram.

Reply 4

Biolover2020

OP

11

Original post by Abedshehabi

Sorry for the late response.

A chromatid is half of a CONDENSED chromosome.

In the human body (for example), a normal cell (not in mitosis) has 23 pairs of chromsomes, which are unwound in the form of chromatin and associated with histones.

In the S phase of interphase, the amount of DNA doubles. During prophase, the chromosomes condense, each having 2 sister chromatids. Each chromatid has an exact DNA copy of the original chromosome. This means each chromosome has double the amount of DNA. However, we still say there are 23 pairs of chromsomes.

Refer to my beautiful MS paint diagram.

Thank u so much this is so helpful!! :smile:

Reply 5

hi I am just wondering, why do we have 80 chromosomes in telophase?

So there is 80 chromosomes and 160 chromatids during prophase. In telophase, the chromatids separate so we should have 160 chromosomes instead (chromatids become chromosomes). There should only be 80 chromosomes in cytokinesis stage right? after the 2 daughter cells are form.

Please someone help me with this. Thankssss

Reply 6

Original post by puprceee

hi I am just wondering, why do we have 80 chromosomes in telophase?
So there is 80 chromosomes and 160 chromatids during prophase. In telophase, the chromatids separate so we should have 160 chromosomes instead (chromatids become chromosomes). There should only be 80 chromosomes in cytokinesis stage right? after the 2 daughter cells are form.
Please someone help me with this. Thankssss

What do you mean by 80 chromosomes in prophase? The cell has 46 condensed chromosomes and 92 chromatids during prophase. During anaphase and telophase, the cell starts the division process, so we have 92 normal chromosomes/92 chromatids. There are only 46 chromosomes/chromatids in each daughter cell after cytokinesis.

(Image credit): https://www.quora.com/What-will-be-the-chromosome-number-in-humans-during-different-phases-of-mitosis-and-meiosis

Reply 7

I’m referring to the question which said there is 80 chromosomes in prophase, it is probably not a human cell

Reply 8

Ohhhh you're right. Yeah there are 80 chromosomes in the trout body cell, not the human cell. But the numbers still work the same (80 condensed chromosomes and 160 chromatids in prophase, 160 normal chromosomes/chromatids during meta and anaphase, and 80 normal chromosomes/chromatids in each daughter cell after cytokinesis).

Reply 9

Original post by Abedshehabi

Ohhhh you're right. Yeah there are 80 chromosomes in the trout body cell, not the human cell. But the numbers still work the same (80 condensed chromosomes and 160 chromatids in prophase, 160 normal chromosomes/chromatids during meta and anaphase, and 80 normal chromosomes/chromatids in each daughter cell after cytokinesis).

Ya that’s what i though, 80 chromosomes in cytokinesis stage, but the answer is 80 chromosomes in telophase, instead of 40, which is why i’m confused

Reply 10

Original post by puprceee

Ya that’s what i though, 80 chromosomes in cytokinesis stage, but the answer is 80 chromosomes in telophase, instead of 40, which is why i’m confused

It would be 40 chromosomes in an EGG cell, which is haploid (only one copy of chromosomes). A trout BODY cell is diploid so it would be 80 chromosomes in the telophase of the trout body cell and 40 chromosomes in an egg cell.

Reply 11

Original post by Abedshehabi

It would be 40 chromosomes in an EGG cell, which is haploid (only one copy of chromosomes). A trout BODY cell is diploid so it would be 80 chromosomes in the telophase of the trout body cell and 40 chromosomes in an egg cell.

so the chromosomes stay the same number throughout the whole cycle in a diploid cell?

Reply 12

Original post by puprceee

so the chromosomes stay the same number throughout the whole cycle in a diploid cell?

Nope. Just refer to this chart and substitute chromosome numbers as needed.

80 normal chromsomes in interphase/80 chromatids
80 condensed chromosomes in prophase and metaphase/160 chromatids
160 normal chromosomes in anaphase and telophase/160 chromatids
80 normal chromosomes/chromatids in each daughter cell after cytokinesis.

Reply 13