mixis

Mixis is a term derived from the Greek for mixing and is used in biology to describe a sexual phase or process of genetic exchange that results in offspring with combined genetic material. In contemporary usage the word is most closely associated with ciliates, a group of single-celled protists such as Paramecium and Tetrahymena.

In ciliates, mixis denotes the sexual stage during which the micronucleus undergoes meiosis, after which the cells exchange haploid micronuclei and participate in conjugation. Following the exchange, the micronuclei fuse (karyogamy) to form a zygotic nucleus, which then divides to restore the germline micronucleus and directs development of a new macronucleus. This sequence leads to genetic recombination and greater variation while the organisms resume their predominantly asexual mode of division.

In broader contexts, mixis is sometimes used to refer more generally to sexual reproduction or gamete fusion in various organisms. Such usage is rarer and can be considered archaic or specialized, with modern discussions often preferring terms like meiosis, fertilization, or conjugation depending on the organism.

See also: sexual reproduction, meiosis, conjugation, karyogamy, ciliates.