[1] Neurospora crassa is used as a model organism because it is easy to grow and has a haploid life cycle that makes genetic analysis simple since recessive traits will show up in the offspring.

Analysis of genetic recombination is facilitated by the ordered arrangement of the products of meiosis in Neurospora ascospores.

[2] Neurospora was used by Edward Tatum and George Wells Beadle in their experiments for which they won the Nobel Prize in Physiology or Medicine in 1958.

As Norman Horowitz reminisced in 2004,[3] "These experiments founded the science of what Beadle and Tatum called 'biochemical genetics'.

Sexual fruiting bodies (perithecia) can only be formed when two mycelia of different mating type come together (see Figure).

Protoperithecia are formed most readily in the laboratory when growth occurs on solid (agar) synthetic medium with a relatively low source of nitrogen.

The sexual cycle is initiated (i.e. fertilization occurs) when a cell (usually a conidium) of opposite mating type contacts a part of the trichogyne (see Figure).

The products of these nuclear divisions (still in pairs of unlike mating type, i.e. A/a) migrate into numerous ascogenous hyphae, which then begin to grow out of the ascogonium.

As the above events are occurring, the mycelial sheath that had enveloped the ascogonium develops as the wall of the perithecium, becomes impregnated with melanin, and blackens.

In a mature ascus containing eight ascospores, pairs of adjacent spores are identical in genetic constitution, since the last division is mitotic, and since the ascospores are contained in the ascus sac that holds them in a definite order determined by the direction of nuclear segregations during meiosis.

These studies usually involved the separate culture of individual ascospores resulting from a single meiotic event and determining the genotype of each spore.

Studies of this type, carried out in several different laboratories, established the phenomenon of "gene conversion" (e.g. see references[11][12][13]).

The two pan-2 mutations B5 and B3 are located at different sites in the pan-2 gene, so that a cross of B5 ´ B3 yields wild-type recombinants at low frequency.

In haploid multicellular fungi, such as N. crassa, meiosis occurring in the brief diploid stage is one of their most complex processes.

In N. crassa, recessive mutations affecting the diploid stage of the life cycle are quite frequent in natural populations.

Thus, outcrossing, promoted by the necessity for the union of opposite mating types, likely provides the benefit of masking recessive mutations that would otherwise be harmful to sexual spore formation (see Complementation (genetics)).