A macronucleus (formerly also meganucleus) is the larger type of nucleus in

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s. Macronuclei are

polyploid Polyploidy is a condition in which the biological cell, cells of an organism have more than two paired sets of (Homologous chromosome, homologous) chromosomes. Most species whose cells have Cell nucleus, nuclei (eukaryotes) are diploid, meaning ...

and undergo direct division without

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

. It controls the non-reproductive cell functions, such as

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

. 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. 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.

References

. Cell nucleus Ciliate biology {{Ciliate-stub

See also

References