Discussion of all aspects of cellular structure, physiology and communication.
Apparently, before counting the # of chromosomes in onion root cells, we can make predictions about the number we are going to find. How is this possible? I am not asking for an answer necessarly, but some pointers would be great!
Apparently due to actively dividing cells at root tips, you'll catch cells at mitosis with 4*n number of chromosomes ( at metaphase for example ).
It seems i don't really understand your question.
Do you mean the following task: "Given name of a species, predict number of chromosomes it has." ?
No, basically in class we looked at cells in mitosis from an onion root.
We found that, on average, there were 18 chromosomes per cell in anaphase.
But they ask us, if we didn't have a microscope, how we could predict the number of chromosomes we were going to find...
Well, that you've got 18 on avarage is due to blurred vision .
Number of chromosome in species is constant ( Usually incorrect number of chromosomes leads to death of the cell ).
Onion's haploid set is 8 chromosomes, diploid set is 8*2=16 chromosomes.
At anaphase you cannot distinguish between sister chromatids thus the apparent number of chromosomes is not changed, that is it remains 16.
Without microscope you can predict the number of chromosomes at any stage of cell cycle by the following rule ( for diploid organism ):
[interphase]--> 2N --[synthesis]--> 4N ---[mitosis]--> 2N ---> [interphase]
where N is haploid number of chromosomes.
Anyway you have to know N from observation or database.
there is a way of aproximating the degree of poliploidy in higher plants, maybe your teacher expects of answer of this type. though i have never heard of poliploid onion..
I would answer so:
1. If the cell observed is in
phase=[interphase..gap1] it has 2*8=16 chromosomes.
2. If the cell observed is in
phase=(synthesis..metaphase) it has 2*8*2=32 chromosomes which appear to be 16 chromosomes.
3. If the cell observed is in
phase=[anaphase..cytokinesis] it has 16+16=32 chromosomes which will be observable because they have been separated by the spindle and moving to opposite directions.
[, ] including ends
(, ) excluding ends
If something's gone wrong with cell devision another numbers can appear, so the above statements are only hypoteses.
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