Explain the meaning of the term "tetrad" as applied to the asci produced by certain fungi.

In the members of the class ascomycetes such as yeast, two haploid yeast cells of two different stains or mating types fuse to form a diploid zygote. Zygote quickly undergoes meiosis or reductional division to form four haploid spores called a tetrad. The tetrad is contained in a sac-like structure called an ascus or fruiting body. Formation of ascus is the characteristic feature of ascomycetes. In the ascus tetrad are not arranged in any specific order. The tetrad are called random or unordered spores. The genetic analysis of the genotypes in the tetrad can tell us about the events during meiosis.