Just a quick clarification me and my friends are disputing. After meiosis I is the cell considered haploid (or is it still diploid?) or is it after the sister chromatids seperate in meiosis II that the cell is haploid?? Any input is appreciated.
Meiosis
- Thread starter preppy36
- Start date
- Joined
- Mar 10, 2005
- Messages
- 80
- Reaction score
- 0
Meiosis I splits the diploid cell into two haploid cells, which in turn go through meiosis II to produce a total of 4 haploid genetically-different cells. Meiosis II is very similar to mitosis, except that in meiosis II the nuclei start out as haploid.
The reason it is haploid after meiosis I is because each cell has one chromosome set. two sister chromatids still connected at the kinetochore (a dyad) is equivalent to one chromosome. they aren't individual chromosomes until they split during meiosis II.
The reason it is haploid after meiosis I is because each cell has one chromosome set. two sister chromatids still connected at the kinetochore (a dyad) is equivalent to one chromosome. they aren't individual chromosomes until they split during meiosis II.
- Joined
- Mar 20, 2005
- Messages
- 1,925
- Reaction score
- 0
I agree with veridisquo and disagree with jkhamlin.
In mitosis, ALL 46 chromosomes line up in the middle of the cell (remember that each chromosome has 2 sister chromatids...i.e. twice as much DNA than normal). After anaphase and telophase, the two daughter cells will also have 46 chromosomes, but will only have a single chromatid.
In meiosis, the 23 pairs of homologous chromosomes line up in the middle. When these split after anaphase I and telophase I, the remaining two cells will each have 23 chromosomes (I.E. haploid), but will have 2 sister chromatids per cell. The cell will then divide again and split the sister chromatids from one another, thus producing 4 gametes with 23 chromosomes.
In mitosis, ALL 46 chromosomes line up in the middle of the cell (remember that each chromosome has 2 sister chromatids...i.e. twice as much DNA than normal). After anaphase and telophase, the two daughter cells will also have 46 chromosomes, but will only have a single chromatid.
In meiosis, the 23 pairs of homologous chromosomes line up in the middle. When these split after anaphase I and telophase I, the remaining two cells will each have 23 chromosomes (I.E. haploid), but will have 2 sister chromatids per cell. The cell will then divide again and split the sister chromatids from one another, thus producing 4 gametes with 23 chromosomes.
- Joined
- Dec 15, 2004
- Messages
- 21
- Reaction score
- 0
jkhamlin said:
No. 'N' does NOT refer to "copies of DNA" but to "number of chromosomes." Therefore, at no point does a somatic or sex cell have 4N chromosomes. A somatic cell goes from 2N (diploid) to 2N (diploid). A sex cell goes from 2N (diploid) before meiosis I, to 2N (diploid) after meiosis I, to N (haploid) after meiosis II.
A chromosome is equivalent to X or ||. In mitosis, a chromosome pair lines up like this:
X
X
and splits like this:
Cell 1
| |
Cell 2
| |
In meiosis I, they line up like this:
XX
and split like this:
Cell 1
X
Cell 2
X
So you can see that after meiosis I, the cell is still diploid.
QofQuimica
Seriously, dude, I think you're overreacting....
Moderator Emeritus
Lifetime Donor
15+ Year Member
- Joined
- Oct 12, 2004
- Messages
- 18,899
- Reaction score
- 4,295
veridisquo said:
This is correct. The cells are haploid after meiosis I.
- Joined
- Nov 2, 2004
- Messages
- 175
- Reaction score
- 0
preppy36 said:
I like to think of it in numbers, something which my bio book kind of assumes is obvious. You have a gamete precursor, which contains 46 chromosomes (23 pairs of chromatids). The whole point of meiosis is to get 4 gametes, each of which contain exactly 23 chromosomes. So... to get 4 cells from 1 cell, the first cell must obviously divide. And since replication is essential to cell division, that means u have a meiosis I & meiosis II. At the start of meiosis (I think its early prophase), the gamete precursor u start out with has made copies of all its chromosomes. So basically u have 92 chromosomes. At the end of meiosis I, u have 2 cells, each of which contain 46 chromosomes. At the end of meiosis II, each of the 2 cells divides, leaving u with 4 cells, and thus 23 chromosomes each. Haploid = 1/2; considering that the gamete precursor u started out with had 46 chromosomes, u have 4 haploid daughter cells.
To answer the original question, it depends on if u take replication into consideration. Remember that somatic cells contain exactly 46 chromosomes each before entering division (this excludes cells like neurons & hepatocytes & i think cardiac muscle fibers, which don't divide, but even these have 46 chromosomes). The gamete precursors also have 46 chromosomes, but not the gametes themselves. Since gametes unite with each other, the usual 46 chromosome number needs to be cut down to 23. Going by the numbers, the only way to have 4 cells at the end of meiosis II, each of which contains 23 chromosomes, is (for the gamete precursor) to have divided into 2 cells at the end of meiosis I, each of which contains 46 chromosomes. But if u take into consideration that the cell (gamete precursor) has made copies of all its chromosomes during prophase I of meiosis I, which leaves the cell with 92 chromosomes, then yes, its haploid after meiosis I, because the two cells contain 46 chromosomes each.
- Joined
- Jan 9, 2003
- Messages
- 1,067
- Reaction score
- 4
That is why I began with IIRC. A quick glance at my Kaplan book reveals that the cells are considered haploid at the end of Meiosis I. N, however does not refer to amount of DNA, and I was not using it as such.KitEKatEli said:
- Joined
- Dec 15, 2004
- Messages
- 21
- Reaction score
- 0
jkhamlin said:
My bad. I looked it up after I got home, too, and you're right. It's haploid after meiosis I, which is reduction division. Meiosis II is just like mitosis but with N chromosomes.
