Reproduction is the process of forming new beings, similar to those that originated them. This can be asexual, when there is only one parent; or sexual, when there is a fusion of gametes from the same individual (self-fertilization) or from different individuals (cross-fertilization). In this case, we are talking about fertilization.
Considering the most common patterns of reproduction, there are species that have developed variations in this modality: these are special cases of reproduction.
PARTHENOGENESIS:
Embryo development from an unfertilized egg. Individuals are usually haploid (drones and yellow scorpions), but may be diploid when not. meiosis occurs or when the polar body joins the egg (eg some species of aphids and butterflies, respectively).
When only male individuals are developed, we call it an arnotoccal parthenogenesis; when they are just females, we speak of telitoca parthenogenesis; and when they are of both sexes, amphitoca.
PEDOGENESIS
Pedogenesis usually occurs in individuals in the larval stage. These can give rise to new larvae, by parthenogenesis or by non-reproductive cells. The flatworm Fasciola hepatica and Schistosoma mansoni can reproduce in this way.
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POLYEMBRYONIA
It can occur in cases of oviparous animals or in parthenogenesis. During mitotic divisions, each cell can give rise to a new individual. The result of this special case of reproduction is the birth of two or more beings, very similar and necessarily of the same sex. Single-egg twins are formed by this process. Humans, armadillos, dogs, rabbits and some insects are examples of species that this reproductive type can occur.
POLYOVULATION
Not all twins are polyembryony: fraternal twins are the result of polyovulation. This occurs when the female releases more than one egg during ovulation, these being fertilized by different sperm. Thus, individuals are genetically different.
By Mariana Araguaia
Graduated in Biology
Would you like to reference this text in a school or academic work? Look:
ARAGUAIA, Mariana. "Parthenogenesis, pedogenesis, polyembryony and polyovulation"; Brazil School. Available in: https://brasilescola.uol.com.br/biologia/casos-especiais2.htm. Accessed on June 27, 2021.
