Molecular patterns of sex determination in the animal kingdom: a comparative study of the biology of reproduction

Abstract

Determining sexual fate is an integral part of reproduction, used as a means to enrich the genome. A variety of such regulatory mechanisms have been described so far and some of the more extensively studied ones are being discussed.For the insect order of Hymenoptera, the choice lies between uniparental haploid males and biparental diploid females, originating from unfertilized and fertilized eggs accordingly. This mechanism is also known as single-locus complementary sex determination (slCSD). On the other hand, for Dipterans and Drosophila melanogaster, sex is determined by the ratio of X chromosomes to autosomes and the sex switching gene, sxl. Another model organism whose sex depends on the X:A ratio, Caenorhabditis elegans, has furthermore to provide for the brief period of spermatogenesis in hermaphrodites (XX) without the benefit of the "male" genes of the sex determination pathway.Many reptiles have no discernible sex determining genes. Their sexual fate is determined by the temperature of the environment during the thermosensitive period (TSP) of incubation, which regulates aromatase activity. Variable patterns of sex determination apply in fish and amphibians. In birds, while sex chromosomes do exist, females are the heterogametic (ZW) and males the homogametic sex (ZZ). However, we have yet to decipher which of the two (Z or W) is responsible for the choice between males and females.In mammals, sex determination is based on the presence of two identical (XX) or distinct (XY) gonosomes. This is believed to be the result of a lengthy evolutionary process, emerging from a common ancestral autosomal pair. Indeed, X and Y present different levels of homology in various mammals, supporting the argument of a gradual structural differentiation starting around the SRY region. The latter initiates a gene cascade that results in the formation of a male. Regulation of sex steroid production is also a major result of these genetic interactions. Similar observations have been described not only in mammals, but also in other vertebrates, emphasizing the need for further study of both normal hormonal regulators of sexual phenotype and patterns of epigenetic/ environmental disruption.

Population Effects of Calcium Phosphate Nanoparticles in Drosophila melanogaster: The Effects of Phase Composition, Crystallinity, and the Pathway of Formation

“…26 This temperature effect on the fruit fly gender falls under the domain of thermosensitive sex selection, which is frequently used in zoology of fish and reptiles. 27 Chronic cold exposure can shift the sex ratio toward a male-biased extreme, 28 whereas spiroplasma endosymbionts, the maternally inherited micro-organisms that infect arthropod species including Drosophila and act as reproductive manipulators by killing exclusively sons of infected mothers may be a factor involved in this variation. 29 Genotoxic effects have been observed in Drosophila dosed with inorganic nanoparticles, 30–32 but they are improbable to occur with CPs, especially at the low concentration in media of 0.3 wt % used in this study.…”

Simultaneous exposure to estrogen and androgen resulted in feminization and endocrine disruption

“…It has long been proposed that epigenetic regulation may play an important role in ESD species in response to environmental influences, leading to the gonad developmental change (Manolakou et al 2006). Plenty of experiment results suggested that epigenetic regulation plays multiple crucial roles in the gonadal differentiation of teleosts and other vertebrates (Navarro-Martin et al 2011, Zhang et al 2013, Parrott et al 2014, Shao et al 2014.…”

Epigenetic regulation of sex ratios may explain natural variation in self-fertilization rates

“…The combination of environmental and genetic factors in sex regulation, a mechanism more common to fish than previously recognized [44], seems the most plausible explanation for our results. Epigenetic regulation of gene expression during gonad differentiation is involved in the adaptive sex reversal observed in some fish and other organisms with genetic sex determination [45]. For example, methylation has been related to sexual reversal in relation to incubation temperature in the half-smooth tongue sole [36].…”