feedback+on+mitosis+video

=Last year's feedback was=

The exercise itself.

1) There was a wide spread of marks from A+ (2 students) to D (2 students, most scoring A-, B or C) 2) Most people produced neat and clear work, with statements in straightforward English, that is always important 3) A common silly mistake was to write something like T. Dubius, when you all know it should be __T. dubius__ 4) The last two questinos about the polyploids themselves was done weakly by many students. This is something you will need to brush up on for the exam, polyploidy is a major part of the course, and you should have examples for any point you wish to make. Both Spartina and Tragopgon are model genera for polyploidy studies.

Students asked these questions while doing the exercise:

I am confused to why the mitotic cell doesn't divide and can cause polyploids when treated with colchicine.


 * It prevents the polymerization of microtubules by binding to tubulin subunits**

How does colchicine prevent the cytokinesis of the cell, I was under the impression from other affectors that these events happen regardless of what stage the chromosomes are at, eg. from the effect of methanol, and their slow segregation, the cleavage furrow simply chops them because they were too slow to move apart. (Is it the presence of SOME at the poles that means it continues?)


 * Without microtubules there is no cell cleavage, or nuclear cleavage, the cleavage furrows normally runs perpendicular to the spindle**

I understand that it causes the depolymerisation of the spindle microtubules so they simply cannot seperate the sister chromatids, but why does the nuclear envelope form around them all creating a polyploid instead of eventually furrowing.


 * The nuclear envelope at telophase forms around chromatin, with or without chromosome division**

Is it because anaphase didn't occur properly and telophase has been skipped?


 * Yes**

On the question sheet we were given for our coursework, the second question asks about the effect of X-ray damage on mitotic cells but the video we watched showed the effects of beta irradiation.


 * You are correct, but the answers are the same. It is just that X rays are less damaging, although more penetrative**

Do dicentrics lead to overall instability of the chromosomes or just that particular one, and why? That is if the cell was able to function with it?


 * Dicentrics do lead to overall genome instability because when the dicentric chromosome is dragged to both poles by the action of the two centromeres the chromatid breaks somewhere in the middle, this leads to sticky chromosome ends without telomeres. These are repared by non-homologous recombination pathways leading to a new dicentric whcih again breaks at the next divsion. This is called the fusion-break-fusion cycle. This was first discovered by Barbara McClintock who later went onto win a Nobel prize for her work on transposable elements**

Finally, I am having slight trouble keeping down to the word limit on some of the questions, for example, for the first question on mitosis, I have reduced and reduced my answer to the very basics of the answer, and I am still on 230 words, I really cannot cut it down anymore, if i do it will be at expense of the fluidity and content of the answer, Will we be penalized for the (minimum) excess of words?


 * Yes, there is an old saying which goes "Dear John, I do not have time for a short letter so here is a long one instead"**