Centromere

The centromere is a constricted region of a chromosome where spindle fibers attach during cell division. After spindle attachment, sister chromatids are pulled to opposite sides of the dividing cell so the daughter cells end up with identical DNA.

• Centromere = the chromosome's constricted region where sister chromatids are held together.
• Spindle fiber microtubules attach to **kinetochore proteins** at the centromeres; kinetochore proteins bind the centromere to spindle microtubules.
• The centromere divides a chromosome into a **short p arm** and a **long q arm** (used in gene/chromosome location notation).

• If you picture an X-shaped chromosome, the thin "pinched" region where the arms join -> the <u>centromere</u>.
• If the question mentions kinetochores attaching spindle microtubules to chromosomes -> the attachment site is at the <u>centromere region</u>.
• If a stem uses labels like Xp or 5q -> <u>p and q arms are defined by the centromere position</u>.