During mitosis, spindle fibres attach to specific small disc-shaped structures present on the surface of the primary constriction of chromosomes. Identify these structures.

Step-by-step solution

Small disc-shaped structures at the surface of the centromeres are called kinetochores. These structures serve as the sites of attachment of spindle fibres to the chromosomes during cell division. The centromere is the primary constriction itself, not the disc-shaped attachment site. The centrosome is the organelle that organizes the spindle fibres, and chromatids are the longitudinal halves of a replicated chromosome. Answer: Kinetochores