Chromosomes are the smallest during anaphase and studied during metaphase. They range in size from 0.5-32 micrometers in length and 0.2-3 micrometers in diameter, with the longest being 32 micrometers in the plant Trillium. Each metaphase chromosome is longitudinally divided into two identical parts called chromatids joined at the centromere. The position of the centromere determines whether the chromosome is metacentric, submetacentric, acrocentric, or telocentric. Telomeres are repetitive units at the ends of chromosomes that maintain structural integrity. Secondary constrictions are associated with nucleoli and are nuclear organizing regions.