Ascus

Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division.

Mitotic divisions within the developing spores populate each resulting cell in septate ascospores with nuclei.

The term ocular chamber, or oculus, refers to the epiplasm (the portion of cytoplasm not used in ascospore formation) that is surrounded by the "bourrelet" (the thickened tissue near the top of the ascus).

That is, the single original diploid cell from which the whole process begins contains two complete sets of chromosomes.

In many cases the asci are formed in a regular layer, the hymenium, in a fruiting body which is visible to the naked eye, here called an ascocarp or ascoma.

By modifying genes coding for spore color and nutritional requirements, the biologist can study crossing over and other phenomena.

The compatible nuclei of the dikaryon merge forming a diploid nucleus that then undergoes meiosis and ultimately internal ascospore formation.

[3] After landing onto a suitable surface, unlike conidia, ascospores of Blumeria graminis showed a more variable developmental patterns.

These findings suggest that mating followed by meiosis is an adaptation for repairing DNA damage in the parental haploid cells in order to allow production of viable progeny ascospores.