The centromere is the chromosome region where the microtubules attach during cell division. In monocentric species, new centromeres can appear during evolution at an ectopic chromosomal location. A new centromere often tends to form near the progenitor centromer, and frequently, the establishment of a new centromere is accompanied by inactivation or loss of function of the old centromere. Initially, newly formed centromeres do not usually contain repeat DNAs but mature gradually through the acquisition and accumulation of repeats. As soon as one or a few repeats invade the novel centromere, their accumulation can be achieved by extended gene conversion during DSB repair. In addition to monocentric eukaryotes, which have a single localized centromere on each chromosome, there are holocentric species, with extended repeat-based or repeat-less centromeres distributed over the entire chromosome length. At least two types of repeat-based holocentromeres exist, one composed of many small repeat-based centromere units (small unit-type), and another one characterized by a few large centromere units (large unit-type). We hypothesize that the transposable element-mediated dispersal of hundreds of short satellite arrays and DNA repair formed the small centromere unit-type holocentromere in e.g. Rhynchospora pubera. The large centromere unit-type of the e.g. plant Chionographis japonica is likely a product of simultaneous DNA double-strand breaks and DNA repair, which initiated the de novo formation of repeat-based holocentromeres via insertion of satellite DNA, derived from extra-chromosomal circular DNAs (eccDNAs).