Kinetochore is present in

$S$ - Statement: During anaphase,the paired chromatids separate.
$R$ - Reason: During anaphase,the spindle fibers shorten,and the centromere splits.

In which stage does the chromatin network condense into chromosomes?

Statement $P$ : Small disc-shaped structures called kinetochores are present on the surface of the centromeres.
Statement $Q$ : Spindle fibers attach to the centromeres of the chromosomes.

Each chromosome at the anaphase stage of a bone marrow cell in our body has

Spindle fibers are primarily composed of which protein?