Katiemick8
Badges: 14
Rep:
?
#1
Report Thread starter 2 years ago
#1
Doing Alevels this month, cannot get my head round mitosis (i umderstand each stage and all the terms, but i only loosely understand the actual process)


A. Just to clarify if you were to look into a cell during prophase, would you see 23 Xs where each side of the X is from the mother and father. Or would you see 46 Xs? Because without two duplicates of each parents chromosomes, how would both daughter cells get the chromosomes from both the mother and father? So 2 Xs for the 1st chromosome etc.

I.e would the 1st autosome be like this: mothers csome -> )( <- fathers csome

Or like this: X <- two copies of mothers csome and another X with two copies of father

Or none lol

B. During telophase, are the copies of both the mothers and fathers chromosomes pulled into different cells, so each cell has a copy of the mother and fathers version of each chromosome?


I appreciate I said everything very awkwardly, but any help would be appreciated if you can decode what ive written 😂 every resource i find seems to contradict other resources
0
reply
luce12341
Badges: 13
Rep:
?
#2
Report 2 years ago
#2
A. You would see 46 Xs because each X is a chromosome made up from two connected chromatids that are produced in DNA replication
B. No because the chromatids joined together are genetically identical - they don't come from the mother and father

I think you're getting confused with meiosis when the daughter cells produced are not genetically identical but in mitosis, during interphase all the DNA replicates so there is still the same amount of chromosomes but twice the amount of DNA so each chromosome in each homologous pair (this is the one where there is one from mother and one from father) replicates and it is these centromeres that get split apart
1
reply
OxFossil
Badges: 17
Rep:
?
#3
Report 2 years ago
#3
(Original post by Katiemick8)
Doing Alevels this month, cannot get my head round mitosis (i umderstand each stage and all the terms, but i only loosely understand the actual process)


A. Just to clarify if you were to look into a cell during prophase, would you see 23 Xs where each side of the X is from the mother and father. Or would you see 46 Xs? Because without two duplicates of each parents chromosomes, how would both daughter cells get the chromosomes from both the mother and father? So 2 Xs for the 1st chromosome etc.

I.e would the 1st autosome be like this: mothers csome -> )( <- fathers csome

Or like this: X <- two copies of mothers csome and another X with two copies of father

Or none lol

B. During telophase, are the copies of both the mothers and fathers chromosomes pulled into different cells, so each cell has a copy of the mother and fathers version of each chromosome?


I appreciate I said everything very awkwardly, but any help would be appreciated if you can decode what ive written 😂 every resource i find seems to contradict other resources
OK - not sure if I can answer your question in the terms you use, but I think I can help.

The "X" shape of chromosomes appears ONLY as mitosis is beginning, and after the chromosome has replicated its DNA.

Most of the time - i.e. during interphase - each chromosome is just one long DNA molecule. It is not doubled. Paternal and maternal alleles are carried on different chromosomes (i.e. different lengths of DNA). However, you cannot easily visualise the chromosomes in interphase, because the double helix and associated proteins are loosely wound - long stretches of it are "unzipped" opened up so that the DNA can be transcribed and proteins produced etc.

That means that when you put DNA stain on a nucleus during interphase, you don't see a bunch of distinct chromosomes, but rather, a vague sort of purple-ish fog. The DNA and the chromosomes are all there, but they are just too relaxed and diffuse to show clearly.

When prophase begins, the DNA of each chromosome replicates along its whole length, to form two identical lengths (chromatids), joined at the centromere. The DNA also now condenses and "shrinks down" so you can now see it clearly. Each chromosome then appears as an X shape - the original chromosome plus the identical twin that it has just manufactured. Each arm of the X is a copy of the corresponding length of the original DNA. Because they are identical, each X is either totally from the mother OR the father. In diploid organisms like humans, each chromosome has a twin - one from each parent. So in humans, you now see 46 Xs, which can be seen to match up into 23 very similar pairs. 23 'Xs' are from one parent, 23 from the other. This is clearly seen when you look at the sex chromosomes (which are a pair). In males, the X chromosome is always from the mother, and the Y chromosome always from the father. In females, one X chromosome is always from the mother, the other X chromosome is from the father.

During telophase, each daughter cell will inherit exactly the same genotype. So the chromosomes align such that the centromere of each "X" disintegrates and one chromatid goes to one pole and the other goes to the other. For a given chromosome pair, one arm from the chromosome inherited from the mother and one arm from the chromosome inherited from the father goes to the same pole.

Once the daughter cells are completely separated and enters interphase, we are back to the original state. The "chromatids" do not replicate, as they are completely functional lengths of DNA just like the parent chromosomes. So they are just called chromosomes again.

Hope that covers it.
1
reply
Katiemick8
Badges: 14
Rep:
?
#4
Report Thread starter 2 years ago
#4
(Original post by lucyv1234)
A. You would see 46 Xs because each X is a chromosome made up from two connected chromatids that are produced in DNA replication
B. No because the chromatids joined together are genetically identical - they don't come from the mother and father

I think you're getting confused with meiosis when the daughter cells produced are not genetically identical but in mitosis, during interphase all the DNA replicates so there is still the same amount of chromosomes but twice the amount of DNA so each chromosome in each homologous pair (this is the one where there is one from mother and one from father) replicates and it is these centromeres that get split apart
(Original post by OxFossil)
OK - not sure if I can answer your question in the terms you use, but I think I can help.

The "X" shape of chromosomes appears ONLY as mitosis is beginning, and after the chromosome has replicated its DNA.

Most of the time - i.e. during interphase - each chromosome is just one long DNA molecule. It is not doubled. Paternal and maternal alleles are carried on different chromosomes (i.e. different lengths of DNA). However, you cannot easily visualise the chromosomes in interphase, because the double helix and associated proteins are loosely wound - long stretches of it are "unzipped" opened up so that the DNA can be transcribed and proteins produced etc.

That means that when you put DNA stain on a nucleus during interphase, you don't see a bunch of distinct chromosomes, but rather, a vague sort of purple-ish fog. The DNA and the chromosomes are all there, but they are just too relaxed and diffuse to show clearly.

When prophase begins, the DNA of each chromosome replicates along its whole length, to form two identical lengths (chromatids), joined at the centromere. The DNA also now condenses and "shrinks down" so you can now see it clearly. Each chromosome then appears as an X shape - the original chromosome plus the identical twin that it has just manufactured. Each arm of the X is a copy of the corresponding length of the original DNA. Because they are identical, each X is either totally from the mother OR the father. In diploid organisms like humans, each chromosome has a twin - one from each parent. So in humans, you now see 46 Xs, which can be seen to match up into 23 very similar pairs. 23 'Xs' are from one parent, 23 from the other. This is clearly seen when you look at the sex chromosomes (which are a pair). In males, the X chromosome is always from the mother, and the Y chromosome always from the father. In females, one X chromosome is always from the mother, the other X chromosome is from the father.

During telophase, each daughter cell will inherit exactly the same genotype. So the chromosomes align such that the centromere of each "X" disintegrates and one chromatid goes to one pole and the other goes to the other. For a given chromosome pair, one arm from the chromosome inherited from the mother and one arm from the chromosome inherited from the father goes to the same pole.

Once the daughter cells are completely separated and enters interphase, we are back to the original state. The "chromatids" do not replicate, as they are completely functional lengths of DNA just like the parent chromosomes. So they are just called chromosomes again.

Hope that covers it.



Thank you both for your detailed reply, that's made it a lot clearer 😊
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

If you do not get the A-level grades you want this summer, what is your likely next step?

Take autumn exams (102)
48.57%
Take exams next summer (31)
14.76%
Change uni choice through clearing (52)
24.76%
Apply to uni next year instead (19)
9.05%
I'm not applying to university (6)
2.86%

Watched Threads

View All