During metaphase, the chromosomes are arranged on the equatorial plate and are attached to spindle fibres. After S phase, can the cell be said to attain the configuration of 4n?

Also, during metaphase, since two spindle fibres (one from say right centriole and other from say left centriole) are attached to one tetrad, so can it be said in a well defined pattern that for a human being, 46*2=92 spindle fibres are formed in order to proceed with mitosis? Also how would the number vary in case of Meiosis I and Meiosis II?


1 Answer 1


The number of spindle fibres is actually more than total number of kinetochore pairs. The fibres attached to kinetochores are called K-fibres and the others are called polar fibres. I cant surely say that there is exactly one K-fibre per kinetochore but as per its definition and from the microscopic images you can conclude that there is one per kinetochore.

In a normal mitotic metaphase there are 2n kinetochore pairs, and as you rightly calculated, there will be 96 K-fibres.

In meiosis-I there is a tetrad which has 2 kinetochore pairs but the ones in sister chromatids behave as a single unit. So there would be 23 fibres.

The fusion of kinetochores of sister chromatids is relaxed in meiosis-II and again a separation would require 23 fibres.

Please have a look at this article. Molecular biology of Meiosis nicely explained: http://www.sciencedirect.com/science/article/pii/S0092867403000837

More about K-fibre formation:



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