During prophase, the nucleus disappears, spindle fibers form, and DNA condenses into chromosomes ( sister chromatids

). During metaphase, the sister chromatids align along the equator of the cell by attaching their centromeres to the spindle fibers.

What stage of mitosis do the spindles form?

The mitotic spindle also begins to develop during prophase. As the cell's two centrosomes move toward opposite poles, microtubules gradually assemble between them, forming the network that will later pull the duplicated chromosomes apart.

Where do spindles form?

At the beginning of nuclear division, two wheel-shaped protein structures called centrioles position themselves at opposite ends of the cell forming cell poles. Long protein fibers called microtubules extend from the centrioles in all possible directions, forming what is called a spindle.