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Könsbestämning hos vertebrater är ett komplext område som har intresserat forskare under en lång tid, trots detta är det i dagens forskningsläge inte helt självklart vad det är som avgör kön. Syftet med denna litteraturstudie är att identifiera och sammanställa kunskap om avgörande könsbestämningsmekanismer utifrån det aktuella forskningsläget. I samband med detta kommer arbetet undersöka hur exempel från könsbestämningssystem hos vertebrater kan användas och tillämpas i biologiundervisning på gymnasiet. Arbetet kom fram till att det är flera gener och proteiner som deltar i könsbestämningen, samt att många av dessa konserverats genom evolutionen. Dock betyder inte detta att alla grupper har samma könsbestämningsmekanismer utan det fanns en stor variation mellan vertebratgrupper. Jämförelser av könsbestämningssystemen visade på nya evolutionära samband mellan genetisk och miljöbetingad könsbestämning. Avslutningsvis konstateras möjliga tillämpningar i biologiundervisningen på gymnasiet. Exempel från olika könsbestämningssystem hos vertebrater kan eventuellt användas för att ge elever nya naturvetenskapliga perspektiv på könsbestämning och utveckla biologilärarens arbete med sexualitet, samtycke och relationer., Sex-determination in vertebrates is a complex area of research that has interested researchers for a long time, still to this day it is not entirely clear what determines sex. The purpose of this literature review is to identify and summarize knowledge about crucial sex-determining mechanisms based on the current state of research. Regarding this review it will investigate how examples from the sex determination system in vertebrates can be used and applied in biology education at high school. The work concludes that there are several genes and proteins that are a part of the sex-determination, and that many of these have been conserved during evolution. However, this does not mean that all the vertebrates have the same sex-determining systems; rather there is a large variance within the vertebrates. Comparison of the sex-determining systems revealed new evolutionary relationships between the genetical- and the environmental sex-determining system. Finally, possible applications in biology education in high school were discussed. Examples from different sex-determining systems in vertebrates could potentially be used to provide students a new scientific perspective of sex-determination and develop the teacher’s work with sexuality, consent and relationships.

Aim: Species with temperature-dependent sex determination (TSD) are particularly vulnerable to climate change because a resultant skew in population sex ratio can have severe demographic consequences and increase vulnerability to local extinction. The Australian central bearded dragon (Pogona vitticeps) has a thermosensitive ZZ male/ZW female system of genetic sex determination (GSD). High incubation temperatures cause reversal of the ZZ genotype to a viable female phenotype. Nest temperatures in the wild are predicted to vary on a scale likely to produce heterogeneity in the occurrence of sex reversal, and so we predict that sex reversal will correlate positively with inferred incubation conditions. Location: Mainland Australia. Methods: Wild-caught specimens of P. vitticeps vouchered in museum collections and collected during targeted field trips were genotypically and phenotypically sexed to determine the distribution of sex reversal across the species range. To determine whether environmental conditions or genetic structure can explain this distribution, we infer the incubation conditions experienced by each individual and apply a multi-model inference approach to determine which conditions associate with sex reversal. Further, we conduct reduced representation sequencing on a subset of specimens to characterize the population structure of this broadly distributed species. Results: Here we show that sex reversal in this widespread Australian dragon lizard is spatially restricted to the eastern part of the species range. Neither climatic variables during the inferred incubation period nor geographic population genetic structure explain this disjunct distribution of sex reversal. The main source of genetic variation arose from isolation by distance across the species range. Main conclusions: We propose that local genetic adaptation in the temperature threshold for sex reversal can counteract the sex-reversing influence of high incubation temperatures in P. vittice

Epigenetics integrates genomic and environmental information to produce a given phenotype. Here, the model of Conserved Epigenetic Regulation of Sex (CERS) is discussed. This model is based on our knowledge on genes involved in sexual development and on epigenetic regulation of gene expression activation and silencing. This model was recently postulated to be applied to the sexual development of fish, and it states that epigenetic and gene expression patterns are more associated with the development of a particular gonadal phenotype, e.g., testis differentiation, rather than with the intrinsic or extrinsic causes that lead to the development of this phenotype. This requires the existence of genes with different epigenetic modifications, for example, changes in DNA methylation levels associated with the development of a particular sex. Focusing on DNA methylation, the identification of CpGs, the methylation of which is linked to sex, constitutes the basis for the identification of Essential Epigenetic Marks (EEM). EEMs are defined as the number and identity of informative epigenetic marks that are strictly necessary, albeit perhaps not sufficient, to bring about a specific, measurable, phenotype of interest. Here, we provide a summary of the genes where DNA methylation has been investigated so far, focusing on fish. We found that cyp19a1a and dmrt1, two key genes for ovary and testis development, respectively, consistently show an inverse relationship between their DNA methylation and expression levels, thus following CERS predictions. However, in foxl2a, a pro-female gene, and amh, a pro-male gene, such relationship is not clear. The available data of other genes related to sexual development such as sox9, gsdf, and amhr2 are also discussed. Next, we discuss the use of CERS to make testable predictions of how sex is epigenetically regulated and to better understand sexual development, as well as the use of EEMs as tools for the diagnosis and prognosis of sex. We arg

Environmental sex determination (ESD) is present in several animal and plant lineages. Diverse factors such as temperature, light or water availability have been described as sex determinants in these organisms. Among plants, ferns frequently display ESD. This work compares the effect of different levels of water availability in two diploid species of the xerophytic fern genus Cheilanthes and in their derived tetraploid, and if they are sensitive to antheridiogen (i.e. maleness-inducing pheromone). Different watering regimes were applied to isolated gametophyte cultures of the three study species. Gametophyte survival, size, gender and sporophyte production were assessed after 13, 18 and 23 weeks of culture. Cultures combining spores and adult gametophytes were established to test the effect of antheridiogen. Isolated gametophytes had an asexual to female to bisexual sequence that did not depend upon the degree of soil moisture. Both gender expression and growth reduction in response to water scarcity of the allotetraploid were more similar to those of one of the diploid parents. In all watering regimes, survival was higher in the allotetraploid, suggesting hybrid vigour, whereas automixis rate was similar in the three species and reached 50 % at high moisture. This breeding system can ensure reproduction in the absence of males. In the three species, female gametophytes produced antheridiogens that enhanced maleness. This promotes a mixed mating system that could be favourable for ferns growing in xeric habitats., Ministerio de Ciencia e Innovación (MICINN), Depto. de Biodiversidad, Ecología y Evolución, Fac. de Ciencias Biológicas, TRUE, pub

Sex determination refers to the developmental programme that commits the embryo to either the male or the female pathway. There are a plethora of mechanisms via which gender is decided. These mechanisms can be classified into three main categories depending on the origin of the primary, genetic, sex-determination signal, which can be zygotic, maternal or environmental. In the dipteran Sciara, the zygotic signal is a consequence of the maternal signal, and this in turn can be a consequence of the environmental signal. This makes Sciara a unique experimental model for studying the evolutionary relationships between the three primary signals triggering sexual development.

Sex determination, due to the obvious association with reproduction and Darwinian fitness, has been traditionally assumed to be a relatively conserved trait. However, research on teleost fishes has shown that this need not be the case, as these animals display a remarkable diversity in the ways that they determine sex. These different mechanisms, which include constitutive genetic mechanisms on sex chromosomes, polygenic constitutive mechanisms, environmental influences, hermaphroditism, and unisexuality have each originated numerous independent times in the teleosts. The evolutionary lability of sex determination, and the corresponding rapid rate of turn-over among different modes, makes the teleost clade an excellent model with which to test theories regarding the evolution of sex determining adaptations. Much of the plasticity in sex determination likely results from the dynamic teleost genome, and recent advances in fish genetics and genomics have revealed the role of gene and genome duplication in fostering emergence and turn-over of sex determining mechanisms.

Many species of fish produced in aquaculture or for the ornamental fish trade exhibit sexual dimorphism in growth, age at maturity, secondary sexual characters, or other traits of interest. This has led to a desire to produce populations of only one sex for commercial ongrowing. Although direct sex reversal via manipulation of sex differentiation is used commercially (e.g., in tilapia aquaculture), in most cases there is a need to understand the sex determination system to some extent and manipulate this to produce monosex fish. Sex determination is the genetic or environmental process that establishes the sex (gender) of an organism, whereas sex differentiation is the process by which an undifferentiated gonad is transformed into an ovary or a testis. Fish are the most diverse group of vertebrates in terms of sex determination, and the number of fish species of interest to aquaculture keeps increasing. Together, these aspects explain the growing interest to understand how sex determination and differentiation produce the sex ratio. This review concentrates on recent research using the tools of molecular biology to broaden our understanding of the different aspects related to fish sex determination, both in model fish species and in species of commercial importance

We compiled information from the literature on the taxonomic distributions in extant teleost fishes of alternative sex-determination systems: male-heterogametic (XY) gonochorism, female-heterogametic (ZW) gonochorism, hermaphroditism, unisexuality, and environmental dependency. Then, using recently published molecular phylogenies based on whole-genomic or partial mitochondrial DNA sequences, we inferred the histories and evolutionary transitions between these reproductive modes by employing maximum parsimony and maximum likelihood methods of phylogenetic character mapping. Across a broad teleost phylogeny involving 25 taxonomic orders, a highly patchy distribution of different sex-determination mechanisms was uncovered, implying numerous transitions between alternative modes, but this heterogeneity also precluded definitive statements about ancestral states for most clades. Closer inspection of family-level and genus-level phylogenies within each of four orders further bolstered the conclusion that shifts in sex-determining modes are evolutionarily frequent and involve a variety of distinct ancestral-descendant pathways. For possible reasons discussed herein, the evolutionary lability of sex-determining modes in fishes contrasts strikingly with the evolutionary conservatism of sex determination within both mammals and birds. © 2006 The Linnean Society of London.

We examined the role played by temperature in the duration of incubation and sex ratio of green turtle hatchlings at Ascension Island, one of the most important green turtle rookeries in the Atlantic. Temperature at control sites at nest depth and in 39 green turtle nests was measured using small temperature recording devices. The sex ratio of hatchlings was ascertained in a sub-sample of monitored nests allowing the description of the relationship between intranest temperature and hatchling sex ratio, demonstrating a pivotal incubation temperature of 28.8°C. The seasonal profile in sex ratio of hatchlings produced on all nesting beaches at Ascension Island was estimated, showing that a female-biased sex ratio would be expected with a female:male ratio of the order of 3:1. The use of nest temperature, air temperature, sand temperature at control sites, and incubation duration as proxies to estimate hatchling sex ratio are discussed.