The region of a chromosome where the two sister chromatids are joined and to which spindle fibres attach is the

Explanation

The centromere holds sister chromatids together and carries the kinetochore, the protein structure the spindle microtubules attach to during division. Telomeres are the protective caps at the chromosome ends that shorten with each replication. Centrioles are separate cytoplasmic structures that organise the spindle rather than part of the chromosome.