English: Tetrahymena conjugation When nutrients are scarce, two individuals (A) pair with each other and begin sexual reproduction (conjugation). (B) The diploid micronucleus in each individual undergoes meiosis to form four haploid nuclei, and three of these are degraded. (C) The remaining haploid nucleus divides mitotically to form two pronuclei in each cell. (D) One of the two pronuclei in each cell is exchanged with the mating partner, and fusion leads to he formation of the diploid zygotic nucleus. (E) The zygotic nucleus divides twice mitotically to form four nuclei. (F) Two nuclei become micronuclei, and the other two differentiate to become macronuclei; the original parental macronucleus is degraded. (G) Cell division occurs and the nuclei are distributed to the daughter cells so that each progeny receives one micronucleus and one macronucleus.