The tutor comments about the reproductive pathways of zygospore fungi, including black bread mold.

With a zygospore fungus, such as black bread mold, the part you see above the surface comprises sporangia (singular: sporangium), which release spores. Spores have n chromosomes; they are haploid. Spores are released into the air. If a spore lands in welcoming conditions, it undergoes mitosis and develops into a new adult.

The more common situation is asexual reproduction, in which a single adult produces spores that repeat its own genetic signature.

Below the surface, the nonreproductive structures are the hyphae, which root throughout the growth medium (bread, for example). Zygospore fungi don’t have male and female individuals, but rather minus and plus. When hyphae from a minus and a plus touch, sexual reproduction occurs. First, each side forms a gametangium at the contact site. Inside each gametangium, gametes are produced. The two gametangia join externally, then, internally, their gametes fuse, forming zygotes, which are diploid (2n). The body in which the zygotes are encased develops a tough protective wall; it’s called a zygospore. This structure can endure adversity until favourable growth conditions resume.

When the zygospore detects promising growth conditions, meiosis occurs within. Then, the new haploid cells undergo mitosis in order to develop new adult bodies from which sporangia develop.

The life cycle described above is haplontic: the adult structures are always haploid (n). Only the zygote is 2n.

Source:

Mader, Sylvia S. Inquiry into Life, 9th ed. Toronto: McGraw-Hill, 2000.

thefreedictionary.com

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.