Macronucleus

A macronucleus (formerly also meganucleus) is the larger type of nucleus in ciliates. Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions such as metabolism. During conjugation, the macronucleus disingtegrates, and a new macronucleus is formed by karyogamy of the micronuclei. The macronucleus contains hundreds of chromosomes, each present in ~50 copies. The macronucleus lacks a mechanism to precisely partition this complex genome equally during nuclear division; thus how the cell manages to maintain a balanced genome after generations of divisions is a mystery. Protozoan nucleus: the larger of two nuclei in most ciliate protozoans, involved in nonreproductive functions such as feeding and metabolism