mitosis

[aka estie]

Hello friends! I am looking over a friend's intro bio practice exam, and I hope you can help with a couple multiple choice questions! I have the second narrowed down to 2, and i think I know the answer for the first, but I am not 100% sure!! :-(

1. If there are 20 chromatids in a cell at metaphase, how many centromeres are there?

2. Which of the following statements is not true?
a. The mitotic spindles in prokaryotic cells are composed of microtubules.
b. Mitosis and cytokinesis are required for asexual reproduction.

Thanks in advance!

Estie

[Peter Pedant]

You have to decide in metaphase whether the structures (!) have separated or not. that is whether they are X or I (the centromere is at the cross of the X and in the middle of the I) that means 10 or 20 depending on where you place metaphase in mitosis.

the pictures of mitosis in your course book should help on this.

a. the word is prokaryotes (and not eukaryotes), does that help ?

[aka estie]

Hi Peter.

My understanding is that the sister chromatids are no longer called that once they are separated, which would be anaphase anyway. My uncertainty comes from the fact that each sister chromatid has a centromere, but is it considered just one when they are joined?

As for the second question, no the word is prokaryotes (i.e. bacteria, archaea). Both of these choices seem incorrect to me since I do not believe prokaryotes have spindles, and I also know that they do not divide by mitisis/cytokinesis. Their asexual reproduction is called binary fission, and it is unknown how the chromosome is distributed to the 'daughter cells'.

Just so you know, I am not trying to get people to answer my homework/exam questions. I have a bachelors and a masters in biology and am currently studying towards my PhD. I am tutoring an undergrad who is taking general biology, and I think these 2 questions on her practice exam are poor questions. I was just looking for some input.

Thanks for trying to help though!

Estie :-)

[aka estie]

Oh I see what you mean for the second one. So would you say that binary fission counts as mitosis/cytokinesis? Her textbook makes a big stink about distinguishing them since binary fission is thought to have predated miotsis. I agree that a is a better answer, but couldn't b be right too?

[ktk]

Hi, The answer to 1. is 10, as each chromosome consists of two chromatids and one centromere joining them together.

The answer to 2. is that a. is not true as prokaryotes do not form spindles. Asexual reproduction (of which binary fission is an example) is as described, mitosis followed by cytokinesis.

Both these questions seem valid to me, and should be suitable for an average AS student.

[aka estie]

Thanks ktk and peter pendant.