These structures were soon recognized also in the division processes of mitosis and meiosis . Magnified , the rod-like chromosomes within one cell vary considerably in size. Many chromosomes have clear constrictions in their rods. The primary constrictions are called centromeres . The ends are called telomeres .
Secondary constrictions are present on some chromosomes.
The number of secondary constrictions agrees closely with the number of nucleoli . Size and shape are used to number and identify chromosomes. Other Pages Interpretations Chromosomes are morphologically variable. They condense and decondense. The condensed form occurs during genetic events such as fertilization and cell division.