During conjugation in ciliates, two cells attach, and their diploid micronuclei undergo meiosis to produce eight haploid nuclei per cell. All but one haploid micronucleus and the macronucleus disintegrate, and the remaining haploid micronucleus undergoes mitosis. The cells then exchange one micronucleus, which fuses with the partner's remaining micronucleus to form a new, genetically distinct diploid micronucleus. This new micronucleus divides mitotically twice to yield four micronuclei, two of which merge to form a new polyploid macronucleus before the genetically altered cells separate.