Dioecy

dioecious, /daɪˈiːʃ(i)əs/ dy-EE-sh(ee-)əs)[2][3] is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants).

It is one method for excluding self-fertilization and promoting allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population.

Spores do not fuse, but germinate by dividing repeatedly by mitosis to give rise to haploid multicellular individuals, the gametophytes, which produce gametes.

[10] The sporophyte generation of seed plants is called dioecious when each sporophyte plant has only one kind of spore-producing organ, all of whose spores give rise either to male gametophytes, which produce only male gametes (sperm), or to female gametophytes, which produce only female gametes (egg cells).

Slightly different terms, dioicous and monoicous, may be used for the gametophyte generation of non-vascular plants, although dioecious and monoecious are also used.

A previously untested hypothesis is that this reduces inbreeding;[27] dioecy has been shown to be associated with increased genetic diversity and greater protection against deleterious mutations.

[28] Regardless of the evolutionary pathway the intermediate states need to have fitness advantages compared to cosexual flowers in order to survive.

[32] Dioecy occurs in almost half of plant families, but only in a minority of genera, suggesting recent evolution.

[37] In the genus Sagittaria, since there is a distribution of sexual systems, it has been postulated that dioecy evolved from monoecy[38] through gynodioecy mainly from mutations that resulted in male sterility.

[44] Monoecy and dioecy in fungi refer to the donor and recipient roles in mating, where a nucleus is transferred from one haploid hypha to another, and the two nuclei then present in the same cell merge by karyogamy to form a zygote.

[45] An individual of a dioecious fungal species not only requires a partner for mating, but performs only one of the roles in nuclear transfer, as either the donor or the recipient.

[45] Dioecy has the demographic disadvantage compared with hermaphroditism that only about half of reproductive adults are able to produce offspring.

Dioecy excludes self-fertilization and promotes allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population.