The spindle is always bipolar, present in both the poles during cell division.
Spindle fibers are associated with centrosomes and are present on both the poles during cell division. For example in budding yeast or somatic cells in humans.
The polarity of the dividing cells is determined by the centrosome itself.
These spindle fibers are contained in centrosome replicates during the cell cycle and the two daughter centrioles occupy each pole.
In organisms that lack centrosomes, the microtubule arranging apparatus, and proteins are responsible for determining polarity.
The microtubules arrange and move the chromosomes in order to segregate the chromosomes between two daughter cells equally from the two ends.
