chromatid and chromosome q

[gomawum]

If acell has 46 chromosomes at the beginning of mitosis, then at anaphase there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosomes

If a cell has 46 chromosomes at the beginning of meiosis, then at anaphase I there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosome


-----------------------
as far as I understands, mitosis does not reduce the chromosome number so 2n -> 2n, which means if there are 42 chromosomes, there has to be 42 chromosomes at the end, where as chromatids are duplicated so 46 -> 92, and become 46 after the division, but the answer for first questions was e..
?????

1st meiotic division is reductive, so 2n -> n, so I assume it to there to be 23 chromosomes, and 92 -> 46 chromatids, but the answer was c.....
??????

I mean can someone clarify the def. of chromosome and chromatid for me?

---

Members don't see this ad.

 

[bigstix808]

If acell has 46 chromosomes at the beginning of mitosis, then at anaphase there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosomes

If a cell has 46 chromosomes at the beginning of meiosis, then at anaphase I there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosome


-----------------------
as far as I understands, mitosis does not reduce the chromosome number so 2n -> 2n, which means if there are 42 chromosomes, there has to be 42 chromosomes at the end, where as chromatids are duplicated so 46 -> 92, and become 46 after the division, but the answer for first questions was e..
?????

1st meiotic division is reductive, so 2n -> n, so I assume it to there to be 23 chromosomes, and 92 -> 46 chromatids, but the answer was c.....
??????

I mean can someone clarify the def. of chromosome and chromatid for me?

Q1 - assuming that DNA synthesis (S-phase) has already occured, at the beginning of mitosis there will be 46 chromosomes (2n) consisting of 92 chromatids (1 chromosome = 2 chromatids). during anaphase, the duplicated chromosomes (made of 2 chromatids) seperate and one copy goes to one side, and one to the other. The chromatids are now termed chromosomes at this point thus why there are 2 x 2n [2 x 46 = 92] chromosomes at anaphase.

Q2 - the thing to remember here is that during METAPHASE I the homologs pair up in the middle, unlike metaphase during mitosis where EACH chromosome lines up in the middle separately. also, the original 46 chromosomes have already duplicated resulting in still 46 chromosomes but 92 chromatids (remember 1 chromosome = 2 chromatids once that chromosome has duplicated). ok, so now that the homologous pairs (2 x 23) are lined up during metaphase I, when anaphase I occurs, those homologs (2 x 23 chromosomes) then separate to each side (23 chromosomes/46 chromatids per side) - thus why there is still the original number of chromosomes (2n=46) at anaphase I.

i hope that made sense

 

[gomawum]

got that, but what about my explanation?
I don't see the way 1.choice b and 2. b are wrong

 

[Willem]

I think the wording of the question is tripping you up. It got me as well when I first read it. You and I are reading the question and wanting it to say "how many chormosomes PER future cell after mitosis/meiosis" and they are wanting to know how many chromosomes there are in sum(the cell has yet to divide). So in mitosis for example your 46(2n) chromosomes end up being 46(2n, only the number of chromatids has halved) chromosomes per future new cell for a sum of 92(2 sets of 2n).

 

[gomawum]

oh I get it..
so they are yet to divide and contain '2 sets of 2n chromosome'

thanks.~

 

[CannonD]

If acell has 46 chromosomes at the beginning of mitosis, then at anaphase there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosomes

If a cell has 46 chromosomes at the beginning of meiosis, then at anaphase I there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosome


-----------------------
as far as I understands, mitosis does not reduce the chromosome number so 2n -> 2n, which means if there are 42 chromosomes, there has to be 42 chromosomes at the end, where as chromatids are duplicated so 46 -> 92, and become 46 after the division, but the answer for first questions was e..
?????

1st meiotic division is reductive, so 2n -> n, so I assume it to there to be 23 chromosomes, and 92 -> 46 chromatids, but the answer was c.....
??????

I mean can someone clarify the def. of chromosome and chromatid for me?

Choice B is wrong in question I because when it undergoes mitosis the result would be 2(2n) and that would be 92 chromosomes right? Ok,next the at anaphase Not Completely separate into 2 cells.As a whole the total is still 92 chromosomes.
Choice B is wrong in question II because during Anaphase I the cell doesn't Completely separate and thus the # of chromosome remains the same. I hope this would help.

 

[reliefe123]

am i dumb...cause i seriously dont understand...during anaphase the daughter chromosomes just get pulled apart...is there not still a total of 23 pairs??it is to my understanding that the 23 pairs get split up into 23on one side and 23 on the other???help me cause i feel dumb as heck right now!!

 

[zvm77]

am i dumb...cause i seriously dont understand...during anaphase the daughter chromosomes just get pulled apart...is there not still a total of 23 pairs??it is to my understanding that the 23 pairs get split up into 23on one side and 23 on the other???help me cause i feel dumb as heck right now!!

Let me rephrase the qes and some thought here from the cliffs ap bio qes book
If we start with a cell 2N=46 at the end of meiosis I each cell will have? 23 chromosones each (cell) and will consist of 2 chromatids At the end of meiosis II each cell will have? 23 chromosomes, each will consist of 1 chomatid reason for this is "at the beginning of meiosis each chromosome has 2 chromatids in anaphase I 2 members of homologous chromosomes move to opp poles. Each daghter formed at the end of meisois I (interphase II) will be haploid n=23 (but with 2 chromatids). During the second division of meiosis @ anaphase II the 2 chromatids separate and move to opp poles. The daghter cells that result will be n=23 (chromosomes, each w/ one chomatid)."
Now from my understanding at the end of meiosis 1 we only have 2 cells (no haploid yet) and as stated above each cell at the end of meiosis 1 has 23 chromosomes so we have 2 (bec only 2 cells at meiosis 1 end) x 23 (chromosomes per cell) = 46

 

[bigstix808]

am i dumb...cause i seriously dont understand...during anaphase the daughter chromosomes just get pulled apart...is there not still a total of 23 pairs??it is to my understanding that the 23 pairs get split up into 23on one side and 23 on the other???help me cause i feel dumb as heck right now!!

you are correct. BUT, during anaphase, both of those pairs of 23 chromosomes are still in ONE cell, hence why the answer to #1 is 92 (46 x 2). they are not considered to be two separate cells until the end of telophase.

 

[reliefe123]

you are correct. BUT, during anaphase, both of those pairs of 23 chromosomes are still in ONE cell, hence why the answer to #1 is 92 (46 x 2). they are not considered to be two separate cells until the end of telophase.

ok...i sort of understand...but dont chrmosomes get synthesized during the s phase...so how come we get more....all we are doing is pullin part chormosomes...

 

[bigstix808]

.

 

[bigstix808]

ok...i sort of understand...but dont chrmosomes get synthesized during the s phase...

YES

...so how come we get more.......

because you just duplicated them during s-phase!! (you're answering your own question)

...all we are doing is pullin part chormosomes...

check it!!😀
vvvvvvvvv
click me

 

[jay47]

If acell has 46 chromosomes at the beginning of mitosis, then at anaphase there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosomes

If a cell has 46 chromosomes at the beginning of meiosis, then at anaphase I there would be a total of
a. 23 chromatids
b. 23 chromosomes
c. 46 chromosomes
d. 46 chromatids
e. 92 chromosome


-----------------------
as far as I understands, mitosis does not reduce the chromosome number so 2n -> 2n, which means if there are 42 chromosomes, there has to be 42 chromosomes at the end, where as chromatids are duplicated so 46 -> 92, and become 46 after the division, but the answer for first questions was e..
?????

1st meiotic division is reductive, so 2n -> n, so I assume it to there to be 23 chromosomes, and 92 -> 46 chromatids, but the answer was c.....
??????

I mean can someone clarify the def. of chromosome and chromatid for me?

The reason that you don't understand is because you NEED TO DEFINE WHAT A CHROMOSOME IS FIRST. A chromosome: a chromatid, or two chromatids with one centromere.

Follow the centromeres in a picture and it will make sense--->

During anaphase of MITOSIS: 46 CHROMOSOMES (each composed of 2 sister chromatids and one centromere) are pulled apart from the metaphase plate. Thus, at one point during anaphase, there will be 92 chromatids in the cell-see http://www.stanford.edu/group/hopes/basics/dna/f_b15mit_ana.jpg

During anaphase of MEIOSIS: 23 TETRADS (each composed of 2 chromosomes, with each chromosome having 2 sister chromatids, are lined up) are lined up at the metaphase plate and pulled apart. When TETRADS are pulled apart, you still have the same number of "chromosomes" because you don't pull sister chromatids apart. See-
http://img.sparknotes.com/content/testprep/bookimgs/sat2/biology/0001/anaphase1.gif

Hope this helps, Jay