During what phase is the cell polyploid? Why is it polyploid at this point--what has happened to create this state and why is it important to the process?
I assume that you mean phase of cell division. First off all i will write down a definition of word polyploid. Polyploid is cell which has two or more pairs of homologus chromozoms. There are two basic types of cell division are meiosis and mitosis
Technicly you can say that in reduction meiosis when chromozomes go from diploity to haploid state (which is first anaphase in this process), but ussually polyplidy occure when something goes wrong in cell division.
The major cause of polyploidy is found to the non disjunction of sister chromatids during the meiotic recombination events. Prior to meiosis chromosome numver doubles followed by chromosome separation during gamete formation (anaphase).
Artificial generation of polyploidy have been found to be useful both in research as well as economic purposes. Colchicine, the chemical which inhibits formation of spidle apparatus is widely used.
Unfortunately colchicine is only used in mitosis. Result of this process is new cultivars of plant specious.