Dormant spores are formed, for example by certain fungi and algae, primarily in response to unfavorable growing conditions.
[citation needed] Reproductive spores are generally the result of cell division, most commonly meiosis (e.g. in plant sporophytes).
Examples are the conidial fungi Aspergillus and Penicillium, for which mitospore formation appears to be the primary mode of reproduction.
The red alga Polysiphonia alternates between mitotic and meiotic sporogenesis and both processes are required to complete its complex reproductive life cycle.
Algae and some fungi (chytrids) often use motile zoospores that can swim to new locations before developing into sessile organisms.
In heterosporous organisms, two types of spores exist: microspores give rise to males and megaspores to females.
In homosporous organisms, all spores look alike and grow into individuals carrying reproductive parts of both genders.
The megaspore undergoes several mitotic divisions to develop into a female gametophyte (for example the seven-cell/eight-nuclei embryo sac in flowering plants).
Some algae, and fungi form resting spores made to survive unfavorable conditions.
The resulting spores are protected through the formation of a thick cell wall and can withstand harsh conditions such as drought or extreme temperatures.
In oomycetes, the zygote forms through the fertilization of an egg cell with a sperm nucleus and enters a resting stage as a diploid, thick-walled oospore.
The germinating oospore undergoes mitosis and gives rise to diploid hyphae which reproduce asexually via mitotic zoospores as long as conditions are favorable.
The term sporogenesis can also refer to endospore formation in bacteria, which allows the cells to survive unfavorable conditions.