I am so confused when a Q asks how many chromatin this cell has given that.... or how many chromosomes.... or any variation of the two.... whats the difference between chromatids, chromatin, chromosomes, sister chromosomes, tetrads... ( I am clearly not a bio major...lol)
stupid question!!!!
- Thread starter NOORALLAH
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I asked my genetics professor when I was studying for the DAT. I hope this helps.
The question is out of the BIO section of Destroyer.
Email Content:
If an organism has a diploid number of 18, how many chromatids are visible at the end of mitotic prophase?
Answer is 36.
Would you be able to explain to me how chromosome/chromatid numbers change in each phase? If you can explain how meiosis changes chromosome/chromatid numbers, that will be great!
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A chromosome is a long double stranded piece of DNA made up of a specific sequence which is complexed with proteins. In the G1 phase of the cell cycle, there is only one copy of each chromosome. In the example you gave below, the diploid number is 18. Since diploids have two copies of each chromosome, this means there are nine different kinds of chromosomes, each present in two copies. (9 X 2 = 18). During S phase, each chromosome replicates to make a pair of identical sister chromatids which are held together in G2 by cohesins. Since each copy of each chromosome has now doubled, the number of chromatids (this is another word for chromosome that is used when the chromosomes are held together by cohesins) is 18 X 2 = 36.
In meiosis, again after premeiotic S phase there would be 36 chromatids. At the first meiotic division, the 9 pairs of sister chromatids (18) segregate to opposite poles. At Meiosis II, the 9 pairs of sister chromatids at each pole separate to give four haploid cells that each contain 9 chromatids (which are now called chromosomes).
The question is out of the BIO section of Destroyer.
Email Content:
If an organism has a diploid number of 18, how many chromatids are visible at the end of mitotic prophase?
Answer is 36.
Would you be able to explain to me how chromosome/chromatid numbers change in each phase? If you can explain how meiosis changes chromosome/chromatid numbers, that will be great!
------------------------------------------------------------------------------------
A chromosome is a long double stranded piece of DNA made up of a specific sequence which is complexed with proteins. In the G1 phase of the cell cycle, there is only one copy of each chromosome. In the example you gave below, the diploid number is 18. Since diploids have two copies of each chromosome, this means there are nine different kinds of chromosomes, each present in two copies. (9 X 2 = 18). During S phase, each chromosome replicates to make a pair of identical sister chromatids which are held together in G2 by cohesins. Since each copy of each chromosome has now doubled, the number of chromatids (this is another word for chromosome that is used when the chromosomes are held together by cohesins) is 18 X 2 = 36.
In meiosis, again after premeiotic S phase there would be 36 chromatids. At the first meiotic division, the 9 pairs of sister chromatids (18) segregate to opposite poles. At Meiosis II, the 9 pairs of sister chromatids at each pole separate to give four haploid cells that each contain 9 chromatids (which are now called chromosomes).
all the words seem so similar... can you define each in one sentence..... like 1 chromatid= 2 chromosomes held together by cohesion....
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visno123 posted this on my thread a while back. This is all you need I think lol.
http://faculty.clintoncc.suny.edu/f...io 101/bio 101 laboratory/mitosis/mitosis.htm
and the thread I posted previously if you want to look:
http://forums.studentdoctor.net/showthread.php?t=850516
http://faculty.clintoncc.suny.edu/f...io 101/bio 101 laboratory/mitosis/mitosis.htm
and the thread I posted previously if you want to look:
http://forums.studentdoctor.net/showthread.php?t=850516
