Difference Between Monoecious and Dioecious Organisms

Difference Between Monoecious and Dioecious Organisms

Sexual reproduction implies the fusion of a female gamete with a male gamete to produce a fertilized zygote which will develop into an individual similar to its parental organism. Depending on the gametes produced, these organisms are classified as monoecious and dioecious. This article explains the difference between the two with suitable examples.
Dual Nature
The common aquatic weed, Hydrilla, exhibits distinct biotypes, of which some are monoecious and some are dioecious, i.e., it has unisexual as well as bisexual strains/varieties.

The system of sex-determination ascertains the development of specific sexual characteristics in an individual organism. This system is yet to be fully understood, but a few pathways have been partially deciphered. In some species, the gender can be determined by examining the genetic constitution of the organism. This holds true for organisms that show the presence of sex chromosomes. In other species, sex can be decided on the basis of the environmental conditions, the organism's relative size, or the gender of other individuals within the population. Some species exhibit two genders, while some exhibit as many as seven genders like the Tetrahymena genus. Alternatively, some species exist that do not possess a permanent gender, rather they change their gender from one to the other during the course of their lifespan. This unique phenomenon is called sequential hermaphroditism.
In comparison, a majority of organisms show the presence of only two genders. However, there exists great diversity in the way these genders are exhibited by various species. Broadly, these organisms can be classified into two types - monoecious and dioecious organisms. The difference between these types are explained in the following table.

Monoecious Organisms Vs. Dioecious Organisms

Monoecious Organisms Dioecious Organisms
Etymology It is derived from the Greek words "mónos" and "oîkos", meaning single house.  It is derived from the Greek words "di" and "oîkos", meaning two houses.
Definition The individual produces the male as well as the female gamete.

The individual produces either the male or the female gamete.

Sexes are present together (hermaphroditism) Sexes are distinct (sexual dimorphism).
Parentage Uniparental reproduction  Biparental reproduction
In Plants In case of bryophytes which display alternation of generations, sexes are observed during the gametophyte stage in the form of antheridia (male) and archegonia (female) clusters.

 In case of bryophytes, sexes are observed during the sporophyte stage in the form of spores that may either be male or female.

In case of higher flowering plants, they are seen in the form of perfect flowers that contain stamens (male) and pistils (female).  In case of higher flowering plants, they are seen in the form of distinct male and female plants. The male plants produce only male gametes, while the female plants only produce the female gametes.
Examples (Plants) Corn Asparagus
Oak trees Papaya trees
Walnut trees Ginkgo biloba trees
In animals Eggs and sperm are produced by the same organism. Some even show presence of both types of external genitals.

Eggs are produced by female organisms and sperm are produced by males. 
Self-fertilization Cross-fertilization
Examples (Animals) Jelly fish Humans
Slugs Dogs
Isolation  Ease in reproduction, even when isolated (species continuity). Cannot reproduce in isolation, i.e., if either of the sexes is absent.
Genetic Variation Inbreeding could cause decrease in genetic variation. Exchange of gametes between two individuals increases heterozygosity and variability.

In higher, more evolved, and complex organisms, a rare and unique phenomenon is observed that is neither monoecious or dioecious. It is called pseudohermaphroditism, and refers to a condition where the individual is born with the primary sexual characteristics of one sex/gender, but later develops the secondary sexual characteristics of a different gender.