Makronuclei

Makronuclei are large, typically diploid or polyploid nuclei found in ciliates, a group of single-celled eukaryotic organisms. These nuclei are distinct from the smaller micronuclei, which are essential for sexual reproduction. The macronucleus, on the other hand, is responsible for the vegetative functions of the cell, controlling daily metabolic activities and gene expression. During asexual reproduction (fission), the macronucleus typically divides amitotically, meaning it elongates and splits without the formation of a spindle apparatus. The DNA content of a macronucleus can be very high, often hundreds of times that of the diploid micronucleus, due to extensive gene amplification and segmental amplification of chromosomes. The genes expressed in the macronucleus are derived from the micronucleus during the process of sexual reproduction (conjugation). The development of a new macronucleus from germ-line micronuclear DNA is a complex and highly programmed process involving extensive DNA rearrangements and selective amplification. The specific ploidy level and structure of macronuclei can vary significantly between different ciliate species.