What is the constricted region of a chromosome where sister chromatids are joined?

The constricted region of a chromosome where sister chromatids are joined is known as the centromere. This structure plays a crucial role during cell division, specifically during the processes of mitosis and meiosis. The centromere holds the sister chromatids together, ensuring that they are separated correctly into daughter cells. This is vital for maintaining the proper number of chromosomes during cell division.

The centromere is also the attachment point for spindle fibers, which pull the chromatids apart and help segregate them into the two new cells that are formed. Its location can vary between different chromosomes, but it is always found in the region that links the two identical chromatids prior to their separation, which is essential for genetic stability.

In contrast, other terms relate to different aspects of chromosome structure but do not refer specifically to the region where sister chromatids are joined. Chromatids are individual strands of a duplicated chromosome, while telomeres are protective caps at the ends of linear chromosomes that prevent degradation. A chromosome, more generally, refers to the entire structure made up of DNA and proteins that carries genetic information. Understanding the function and structure of the centromere is key to grasping how chromosomes behave during cell division.