Sex reversal is a biological process whereby the pathway directed towards the already determined-sex fate is flipped towards the opposite sex, creating a discordance between the primary sex fate and the sex phenotype expressed. The process of sex reversal occurs during embryonic development or before gonad differentiation. In

GSD GSD may refer to: Schools * Georgia School for the Deaf, in Cave Spring, Georgia, United States * Harvard Graduate School of Design Science and medicine * Genetic significant dose * Global Species Database * Glutathione synthetase deficiency * ...

species sex reversal means that the sexual phenotype is discordant with the genetic/chromosomal sex. In TSD species sex reversal means that the temperature/conditions that usually trigger the differentiation towards one sexual phenotype are producing the opposite sexual phenotype. Sex reversal can occur naturally, by mutations, or can be induced artificially. Sex reversal can be genetically or hormonally induced in laboratory. It can also occur artificially by exposure to endocrine disruptors such as

pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...

s, including

herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

s, which can act as estrogen promoters or inhibitors, for instance by altering

aromatase Aromatase (), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze many ...

expression.

In vertebrates

In gonochoristic fishes

In gonochoristic fishes, the sex can be determined genetically, environmentally or by a combination of both. In fishes, primary sexual fate can be susceptible to alteration by hormones exposure and multiple environmental factors, such as population density, water pH, or temperature. Those conditions can affect the gonad development and differentiation, which can lead to sex reversal. In medaka fish, where sex reversal has been documented show a shared gene related to normal male development, the ''dmy'' gene. In wild populations, genetically female fate can be phenotypically reversed to males if they carry the ''dmy'' gene or a mutated ''dmy'' gene and genetic males can be reversed to females if they lack the ''dmy'' gene.

Induced reversal in aquaculture industry

In aquaculture, sex control is important due to the role of sex in growth and reproduction. In fishes, growth rates can be different between sexes. These differences can affect their economic value. Producing a monosex fish population can improve product quality and therefore generates higher financial profit. Hormone-induced sex reversal is the most frequent method used in aquaculture. It consists of exposing sexually undifferentiated fishes to

sex steroid Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effect ...

s. There are other methods to induced sex reversal in fishes such as chromosomal/genetic manipulation, hybridization, or treatments influencing sex determination or gonad differentiation (e.g. temperature, population density, pH, social factors).

In amphibians

Sex is genetically determined in

amphibian Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...

s. Temperature-induced sex reversal has been documented in some species of anuran and caudate amphibians. Temperature only can have an effect on sex differentiation during a window period called thermosensitive period (TSP) which varies among species. Tadpoles or larvae exposed to specific higher or lower temperatures, depending on the temperature thresholds of the species, can differentiate gonads that do not align with their primary sexual fate. Amphibian sex reversal can be also induced by exposure to sex steroid and pollutants. Endocrine disruptors can affect gonad differentiation, and therefore induce sex reversal. Exposure to ethylnyl estradiol (EE₂) and bisphenol A (BPA) induces feminizing effects. Masculinizing effects can be induced by exposure to the drug trenbolone, used in cattle. Research in wild populations of the North American green frog has demonstrated that sex reversal is common. This work shows that genetic females sex reverse into phenotypic males and that genetic males sex reverse into phenotypic females, providing evidence that sex reversal can be bidirectional in amphibians. While endocrine disrupting chemical contamination is known from laboratory experiments to cause sex reversal in amphibians, sex reversal in green frogs occurs irrespective of contamination, suggesting sex reversal is a natural process in amphibians

In reptiles

Sex in reptiles can be determined genetically (GSD), environmentally (ESD) or by an interaction of both. Sex reversal has been documented in detail in wild populations of the central bearded dragon ''

Pogona vitticeps The central bearded dragon (''Pogona vitticeps''), also known as the inland bearded dragon, is a species of agamid lizard found in a wide range of arid to semiarid regions of eastern and central Australia. Taxonomy ''Pogona vitticeps'' was firs ...

,'' and in the eastern three-lined skink '' Bassiana duperreyi.'' In these species, their genetically determined sex is overridden by temperature influence. Sex reversal in reptiles can be induced by hormonal manipulation, treatments influencing sex determination (e.g. temperature) or by inhibition of the

gene (CYP19A1) which causes sex reversal from female to male phenotype.

In birds

In birds, sex reversal has been documented in natural and experimental conditions.

Sex steroid Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effect ...

manipulation can induced sex reversal in birds. Aromatase inhibitors injected into chicken eggs before the gonadal differentiation stage induce testis development in ZW embryos.

In mammals

Sex reversal in mammals has been documented in domestic species such as

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...

water buffalo The water buffalo (''Bubalus bubalis''), also called the domestic water buffalo or Asian water buffalo, is a large bovid originating in the Indian subcontinent and Southeast Asia. Today, it is also found in Europe, Australia, North America, So ...

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s, pigs,

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...

s, etc. Sex reversal in these species usually relates to genetic changes and the resulting phenotype is often associated with gonadal malformation. Natural sex reversal without disruptive effects on fertility has been documented in several rodents, including '' Myopus schisticolor, Dicrostonyx torquatus,

Akodon ''Akodon'' is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west ...

, Mus minutoides, Microtus cabrerae.'' In these species some individuals genetically determined as males develop typical ovarian structure. In these rodents species, sex reversal mainly occurs after mutational events.

References

{{Sex determination and differentiation Embryology Sexuality