Ascus,
(plual asci) is a sac-like structure containing a tetrad of four spores (or ascospores).

Heterothallic,
strains of yeast have cross-compatible mating types and are stable both as haploids and diploids.

Homothallic,
strains of yeast give rise to tetrads containing four potentially self-fertile members, because the transient haploid cells switch their mating types, and thus have only a stable diplophase.

Plasmid shuffle,
is a procedure for screening of mutations, derived from a mutagenized plasmid, requiring the loss of a second plasmid to assay for the recessive mutations.

Shuttle vectors,
are vectors that can be propagated in both yeast and E. coli.

Tetrad,
is the four products of meiosis.

Two-hybrid system,
is a genetic assay used in yeast for detection of protein-protein interactions.