Biological process

A mitotic cell cycle in which chromosomes are replicated and sister chromatids separate, but spindle formation, nuclear membrane breakdown and nuclear division do not occur, resulting in an increased number of chromosomes in the cell.

endomitosis

Note that this term should not be confused with 'abortive mitotic cell cycle ; GO:0033277'. Although abortive mitosis is sometimes called endomitosis, GO:0033277 refers to a process in which a mitotic spindle forms and chromosome separation begins.