A macronucleus (formerly also meganucleus) is the larger type of nucleus in ciliates.
Macronuclei are polyploid and undergo direct division without mitosis.
During conjugation, the macronucleus disintegrates, and a new one is formed by karyogamy of the micronuclei.
Macronuclei contain hundreds to thousands of chromosomes, each present in many copies.
[1][2] There is no 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 unknown.