Chromosomes are of five types according to the number of centromeres.
(i) Acentric Chromosome: A chromosome which does not have a centromere is called an acentric chromosome. It is the fragile part of the chromosome. It does not participate in cell division as it does not have a centromere.
(ii) Monocentric Chromosome: Chromosome having only one centromere is called monocentric chromosome. Chromosomes in most species are monocentric.
(iii) Dicentric Chromosome: A chromosome having two centromeres is called a dicentric chromosome. Wheat, Bhutra, yeast and Dsophila fly have dicentric chromosomes.
(iv) Polycentric Chromosome: A chromosome having more than two centromeres is called a polycentric chromosome. Banana plants, Luzula purpurea, Spirogyra and roundworms have polycentric chromosomes.
(v) Diffuse Chromosomes: If the centromeres are isolated in a chromosome, it is called diffuse chromosome. Banana plants have diffuse chromosomes.