Frequent independent origins of environmental sex determination (ESD) are assumed within amniotes. However, the phylogenetic distribution of sex‐determining modes suggests that ESD is likely very ancient and may be homologous across ESD groups. Sex chromosomes are demonstrated to be old and stable in endothermic (mammals and birds) and many ectothermic (non‐avian reptiles) lineages, but they are mostly non‐homologous between individual amniote lineages. The phylogenetic pattern may be explained by ancestral ESD with multiple transitions to later evolutionary stable genotypic (...) sex determination. It is pointed out here that amniote ESD shares several key aspects with sequential hermaphroditism of fishes such as a lack of sex differences in genomes, biased population sex ratios, and potentially also molecular mechanism related to general stress responses. Here, it is speculated that ESD evolves via a heterochronic shift of the sensitive period of sex change from the adult to the embryonic stage in a hermaphroditic amniote ancestor. Also see the video abstract here https://youtu.be/q2mjtlCefu4. (shrink)

Sex‐determining factors are usually assumed to be either genetic or environmental. The present paper aims at drawing attention to the potential contribution of developmental noise, an important but often‐neglected component of phenotypic variance. Mutual inhibitions between male and female pathways make sex a bistable equilibrium, such that random fluctuations in the expression of genes at the top of the cascade are sufficient to drive individual development toward one or the other stable state. Evolutionary modeling shows that stochastic sex determinants (...) should resist elimination by genetic or environmental sex determinants under ecologically meaningful settings. On the empirical side, many sex‐determination systems traditionally considered as environmental or polygenic actually provide evidence for large components of stochasticity. In reviewing the field, I argue that sex‐determination systems should be considered within a three‐ends continuum, rather than the classical two‐ends continuum. (shrink)

The adaptive significance of temperature‐dependent sex determination (TSD) in reptiles remains unknown decades after TSD was first identified in this group. Concurrently, there is growing concern about the effect that rising temperatures may have on species with TSD, potentially producing extremely biased sex ratios or offspring of only one sex. The current state‐of the‐art in TSD research on sea turtles is reviewed here and, against current paradigm, it is proposed that TSD provides an advantage under warming climates. By means (...) of coadaptation between early survival and sex ratios, sea turtles are able to maintain populations. When offspring survival declines at high temperatures, the sex that increases future fecundity (females) is produced, increasing resilience to climate warming. TSD could have helped reptiles to survive mass extinctions in the past via this model. Flaws in research on sex determination in sea turtles are also identified and it is suggested that the development of new techniques will revolutionize the field. (shrink)

For many species that reproduce sexually, how sex is expressed at different points across lifespan is highly contingent and dependent on various environmental factors. For example, in many species of fish, environmental cues can trigger a natural process of sex transition where a female transitions to male. For many species of turtle, incubation temperature influences the likelihood that turtle eggs will hatch males or females. What is the case for Homo sapiens? Is human sex expression influenced by contingent (...) environmental factors like we see in fish and turtles, with whom we share common ancestry and DNA? Our paper explores the current biological science of sex determination and how it applies to philosophical and theological accounts of the human person. We argue that while human sex determination is not susceptible to environmental cues to the same degree we see in other species, there is sufficient variability among the pathways of human sex development to complicate simplistic biological categories of male and female. (shrink)

Two prevailing paradigms explain the diversity of sex-determining modes in reptiles. Many researchers, particularly those who study reptiles, consider genetic and environmental sex-determining mechanisms to be fundamentally different, and that one can be demonstrated experimentally to the exclusion of the other. Other researchers, principally those who take a broader taxonomic perspective, argue that no clear boundaries exist between them. Indeed, we argue that genetic and environmental sex determination in reptiles should be seen as a continuum of states (...) represented by species whose sex is determined primarily by genotype, species where genetic and environmental mechanisms coexist and interact in lesser or greater measure to bring about sex phenotypes, and species where sex is determined primarily by environment. To do otherwise limits the scope of investigations into the transition between the two and reduces opportunities to use studies of reptiles to advance understanding of vertebrate sex determination generally. © 2004 Wiley Periodicals, Inc. (shrink)

We hypothesize that under the predicted scenario of climate change epigenetically mediated environmental sex determination could become an epigenetic trap. Epigenetically regulated environmental sex determination is a mechanism by which species can modulate their breeding strategies to accommodate environmental change. Growing evidence suggests that epigenetic mechanisms may play a key role in phenotypic plasticity and in the rapid adaptation of species to environmental change, through the capacity of organisms to maintain a non‐genetic plastic memory (...) of the environmental and ecological conditions experienced by their parents. However, inherited epigenetic variation could also be maladaptive, becoming an epigenetic trap. This is because environmental sex determination can alter sex ratios by increasing the survival of one of the sexes at the expense of negative fitness consequences for the other, which could lead not only to the collapse of natural populations, but also have an impact in farmed animal and plant species. (shrink)

Graphical AbstractSquamates may be an attractive group in which to study the influence of sex chromosomes on speciation rates because of the repeated evolution of heterogamety (both XY and ZW), as well as an apparently large number of taxa with environmental sex-determination.

Sex reversal, a mismatch between phenotypic and genetic sex, can be induced by chemical and thermal insults in ectotherms. Therefore, climate change and environmental pollution may increase sex‐reversal frequency in wild populations, with wide‐ranging implications for sex ratios, population dynamics, and the evolution of sex determination. We propose that reconsidering the half‐century old theory “Witschi's rule” should facilitate understanding the differences between species in sex‐reversal propensity and thereby predicting their vulnerability to anthropogenic environmental change. The idea is (...) that sex reversal should be asymmetrical: more likely to occur in the homogametic sex, assuming that sex‐reversed heterogametic individuals would produce new genotypes with reduced fitness. A review of the existing evidence shows that while sex reversal can be induced in both homogametic and heterogametic individuals, the latter seem to require stronger stimuli in several cases. We provide guidelines for future studies on sex reversal to facilitate data comparability and reliability. (shrink)

Sex allocation research has primarily focused on offspring sex‐ratio adjustment by mothers. Yet, fathers also benefit from producing more of the sex with greater fitness returns. Here, we review the state‐of‐the art in the study of male‐driven sex allocation and, counter to the current paradigm, we propose that males can adaptively influence offspring sex ratio through a wide variety of mechanisms. This includes differential production and motility of X‐ versus Y‐bearing sperms in mammals, variation in seminal fluid composition in haplo‐diploid (...) invertebrates, and epigenetic mechanisms in some fish and lizards exhibiting environmental sex determination. Conflicts of interest between mothers and fathers over offspring sex ratios can emerge, although many more studies are needed in this area. While many studies of sex allocation have focused on adaptive explanations with little attention to mechanisms, and vice versa, the integration of these two topics is essential for understanding male‐driven sex allocation. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:The Environmental Genome Project and BioethicsRichard R. Sharp (bio) and J. Carl Barrett (bio)Eight years ago, the Kennedy Institute of Ethics Journal published a brief selection by Eric Juengst (1991) entitled “The Human Genome Project and Bioethics.” That essay introduced and described the Ethical, Legal, and Social Implications (ELSI) Program at the National Center for Human Genome Research. 1 Since that time, the ELSI program has grown to (...) become one of the largest and most well regarded bioethics programs in the country, sponsoring the work of hundreds of researchers and coordinating bioethics activities both nationally and internationally (Marshall 1996; Meslin, Thomson, and Boyer 1997). In 1991, however, Juengst, the first director of the ELSI program, had no way of anticipating these developments. Juengst’s goal in his essay was simply to highlight some of the moral and social issues that were emerging as focal points for the ELSI program. Looking back, the issues he outlined may seem vague and overly broad. At the time, however, the essay served an important purpose, to identify areas requiring additional study and thereby to serve as a guide to others interested in joining in these discussions.In many ways, Juengst’s article serves as an inspiration to those of us working on a new bioethics project. The National Institute of Environmental Health Sciences (NIEHS) recently launched a multi-year project aimed at better understanding genetic influences on environmentally associated diseases (Albers 1997; Brown and Hartwell 1998; Cannon 1997; Kaiser 1997). This project, known as the Environmental Genome Project (EGP), plans to identify and study a number of common genetic variants that may play an important role in determining how individuals respond to environmental exposures. NIEHS hopes that the information learned through the EGP will be instrumental in developing more effective disease-prevention strategies and intervention programs. Following the precedent developed in connection with the Human Genome Project, NIEHS also plans to address the moral and social implications of the EGP. Efforts in this regard include sponsoring workshops and conferences to address such issues, as well as supporting research on the ethical, legal, and social implications of the EGP. Through this work, NIEHS hopes to anticipate potential problems before [End Page 175] they arise and to develop policies that maximize the benefits of the research while avoiding potential misuses of the information learned.In exploring the social implications of the EGP, we at NIEHS are very fortunate to be able to draw upon the work being done by the ELSI program at the National Human Genome Research Institute (NHGRI), as well as the ever-expanding bioethics literature that has been sparked by the ELSI program. Still, there is much to be done and this is an exciting time for those of us involved with the EGP. Many of the ethical, legal, and social implications of the project are only beginning to become clearer, and several of these issues appear quite different from the sorts of concerns that have previously been discussed in connection with other types of genetic research.This essay highlights some of the ethical, legal, and social implications that are emerging as important focal points for the Environmental Genome Project. Like Juengst’s 1991 paper, the goal of this article is to provide an overview of current areas of interest and to encourage others to join us in thinking about these difficult issues.The Environmental Genome ProjectIndividuals differ greatly in their responses to chemicals, drugs, radiation, smoking, alcohol, and other environmental exposures. These differential responses are the result of complex interactions between many factors, including an individual’s genetic make-up, age, sex, nutritional status, and overall health. The EGP aims to better understand the genetic basis of differential responses to environmental exposures. The vast majority of diseases, many forms of cancer, for example, are the consequence of both environmental and genetic contributions (Perera 1997). Hence, understanding the relationships between genetic variation and response to environmental exposure is important for understanding the causes of human disease and is crucial for the development of effective disease-prevention strategies.The EGP and projects like it represent a new stage of genomic research. It is expected that the Human Genome Project will complete... (shrink)

Sex‐specific transcriptional and epigenomic profiles are detectable in the embryo very soon after fertilization. I propose that in male (XY) and female (XX) pre‐implantation embryos sex chromosomes establish sexually dimorphic interactions with the autosomes, before overt differences become apparent and long before gonadogenesis. Lineage determination restricts expression biases between the sexes, but the epigenetic differences are less constrained and can be perpetuated, accounting for dimorphisms that arise later in life. In this way, sexual identity is registered in the epigenome (...) very early in development. As development progresses, sex‐specific regulatory modules are harbored within shared transcriptional networks that delineate common traits. In reviewing this field, I propose that analyzing the mechanisms for sexual dimorphisms at the molecular and biochemical level and incorporating developmental and environmental factors will lead to a greater understanding of sex differences in health and disease. (shrink)

Sex chromosomes are advantageous to mammals, allowing them to adopt a genetic rather than environmental sex determination system. However, sex chromosome evolution also carries a burden, because it results in an imbalance in gene dosage between females (XX) and males (XY). This imbalance is resolved by X dosage compensation, which comprises both X chromosome inactivation and X chromosome upregulation. X dosage compensation has been well characterized in the soma, but not in the germ line. Germ cells face a (...) special challenge, because genome wide reprogramming erases epigenetic marks responsible for maintaining the X dosage compensated state. Here we explain how evolution has influenced the gene content and germ line specialization of the mammalian sex chromosomes. We discuss new research uncovering unusual X dosage compensation states in germ cells, which we postulate influence sexual dimorphisms in germ line development and cause infertility in individuals with sex chromosome aneuploidy. (shrink)

Animal and plant species exhibit an astonishing diversity of sexual systems, including environmental and genetic determinants of sex, with the latter including genetic material in the mitochondrial genome. In several hermaphroditic plants for example, sex is determined by an interaction between mitochondrial cytoplasmic male sterility (CMS) genes and nuclear restorer genes. Specifically, CMS involves aberrant mitochondrial genes that prevent pollen development and specific nuclear genes that restore it, leading to a mixture of female (male‐sterile) and hermaphroditic individuals in the (...) population (gynodioecy). Such a mitochondrial‐nuclear sex determination system is thought to be rare outside plants. Here, we present one possible case of CMS in animals. We hypothesize that the only exception to the strict maternal mtDNA inheritance in animals, the doubly uniparental inheritance (DUI) system in bivalves, might have originated as a mitochondrial‐nuclear sex‐determination system. We document and explore similarities that exist between DUI and CMS, and we propose various ways to test our hypothesis. (shrink)

Graphical AbstractIn article number 2000050, Barbora Straková et al. speculate that environmental sex determination in amniotes evolves via a heterochronic shift of sex change from the adult to the embryonic stage in a hermaphroditic ancestor. Subsequently, the loss of responsiveness to environmental stimuli (stress) led to genotypic sex determination, where the sex is decided at conception. Cover image by Tereza Unzeitigova.

Spatial and mathematical abilities may be “sex-limited” traits. A sex-limited trait has the same determinants of variation within the sexes, but the genetic or environmental effects would be differentially expressed in males and females. New advances in structural equation modeling allow means and variation to be estimated simultaneously. When these statistical methods are combined with a genetically informative research design, it should be possible to demonstrate that the genes influencing spatial and mathematical abilities are sex-limited in their expression. This (...) approach would give an empirical confirmation of Geary's evolutionary speculations. (shrink)

Sex‐determining mechanisms appear to be very diverse in invertebrates. Haplodiploidy is a widespread mode of reproduction in insects: males are haploid and females are diploid. Several models have been proposed for the genetic mechanisms of sex determination in haplodiploid Hymenoptera. Although a one‐locus multi‐allele model is valid for several species, sex determination in other species cannot be explained by any of the existing models. Evidence for and predictions of two recently proposed models are discussed. Some genetic and molecular (...) approaches are proposed to study sex determination in Hymenoptera. (shrink)

The pathway that controls sexual fate in the nematode Caenorhabditis elegans has been well characterized at the molecular level. By identifying differences between the sex‐determination mechanisms in C. elegans and other nematode species, it should be possible to understand how complex sex‐determining pathways evolve. Towards this goal, orthologues of many of the C. elegans sex regulators have been isolated from other members of the genus Caenorhabditis. Rapid sequence evolution is observed in every case, but several of the orthologues appear (...) to have conserved sex‐determining roles. Thus extensive sequence divergence does not necessarily coincide with changes in pathway structure, although the same forces may contribute to both. This review summarizes recent findings and, with reference to results from other animals, offers explanations for why sex‐determining genes and pathways appear to be evolving rapidly. Experimental strategies that hold promise for illuminating pathway differences between nematodes are also discussed. BioEssays 25: 221–231, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

Recent molecular studies of mammalian sexual determination have been focused on gene expression in the gonadal ridge at the time of appearance of sexual dimorphism: the critical time defined by the ‘Jost principle’. Three lines of evidence suggest that, instead, sex determination may start shortly after conception: (1) the XY preimplantation embryo usually develops more rapidly than the XX preimplantation embryo (this phenotype has been linked to the Y chromosome and will be termed ‘Growth factor Y’); (2) the (...) gene for testis determination, SRY/Sry, and the closely linked genes ZFY/Zfy and Smcy, are transcribed in the preimplantation embryo; and (3) male and female preimplantation embryos are antigenically distinguishable, indicating sex differences in gene expression. The data to support these assertions are reviewed. Possible relationships of these three phenomena to each other and to sex differentiation are discussed. Similarities in mechanisms of sexual determination between marsupial and eutherian mammals are hypothesized. Problems with interpreting male sexual differentiation as being solely due to testosterone and Müllerian inhibiting substance (MIS) are discussed. (shrink)

In mammals, the Y chromosome induces testis formation and thus male sexual development; in the absence of a Y chromosome, gonads differentiate into ovaries and female development ensues. Molecular genetic studies have identified the Y‐located testis determining gene SRY as well as autosomal and X‐linked genes necessary for gonadal development. The phenotypes resulting from mutation of these genes, together with their patterns of expression, provide the basis for establishing a hierachy of genes and their interactions in the mammalian sex (...) class='Hi'>determination pathway. (shrink)

Not all vertebrates share the familiar system of XX:XY sex determination seen in mammals. In the chicken and other birds, sex is determined by a ZZ:ZW sex chromosome system. Gonadal development in the chicken has provided insights into the molecular genetics of vertebrate sex determination and how it has evolved. Such comparative studies show that vertebrate sex‐determining pathways comprise both conserved and divergent elements. The chicken embryo resembles lower vertebrates in that estrogens play a central role in gonadal (...) sex differentiation. However, several genes shown to be critical for mammalian sex determination are also expressed in the chicken, but their expression patterns differ, indicating functional plasticity. While the genetic trigger for sex determination in birds remains unknown, some promising candidate genes have recently emerged. The Z‐linked gene, DMRT1, supports the Z‐dosage model of avian sex determination. Two novel W‐linked genes, ASW and FET1, represent candidate female determinants. BioEssays 26:120–132, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

Endosymbiotic bacteria can directly manipulate their host's sex determination towards the production of female offspring.

Sex chromosomes in plants have been known for a century, but only recently have we begun to understand the mechanisms behind sex determination in dioecious plants. Here, we discuss evolution of sex determination, focusing on Silene latifolia, where evolution of separate sexes is consistent with the classic “two mutations” model—a loss of function male sterility mutation and a gain of function gynoecium suppression mutation, which turned an ancestral hermaphroditic population into separate males and females. Interestingly, the gynoecium suppression (...) function in S. latifolia evolved via loss of function in at least two sex‐linked genes and works via gene dosage balance between sex‐linked, and autosomal genes. This system resembles X/A‐ratio‐based sex determination systems in Drosophila and Rumex, and could represent a steppingstone in the evolution of X/A‐ratio‐based sex determination from an active Y system. (shrink)

Sex chromosomes can differ between species as a result of evolutionary turnover, a process that can be driven by evolution of the sex determination pathway. Canonical models of sex chromosome turnover hypothesize that a new master sex determining gene causes an autosome to become a sex chromosome or an XY chromosome pair to switch to a ZW pair (or vice versa). Here, a novel paradigm for the evolution of sex determination and sex chromosomes is presented, in which there (...) is an evolutionary transition in the master sex determiner, but the X chromosome remains unchanged. There are three documented examples of the novel paradigm, and it is hypothesized that a similar process could happen in a ZW sex chromosome system. Three other taxa are also identified where the novel paradigm may have occurred, and how it could be distinguished from canonical trajectories in these and additional taxa is also described. (shrink)

Direction of the embyro's head rotation is determined by asymmetrical expression of several genes (such as shh, Nodal, lefty, and FGF8) in Hensen's node. This genetically determined head-turning bias provides a base for light-aligned population lateralization in chicks, in which the direction of the lateralization is determined by genetic factors and the degree of the lateralization is determined by environmental factors.

Prenatal diagnostic technologies have been used for the purpose of detecting sex—leading to abortion of female fetuses—and have posed new challenges to the already difficult question of social justice for women in India. This article reports findings from a case study conducted with 25 women who had used prenatal diagnostic technologies for sex determination.Against the common belief that Indian society is “improving” because of 21st-century medical technology, this case study shows that the social context has given a patriarchal value (...) to such advanced technology in India. Furthermore, it sheds light on why prenatal diagnostic technologies have taken a different route in India.It shows that reasons for accepting the use of prenatal diagnostic technologies for sex determination by women are diverse and complex. (shrink)

In many species of reptiles, sex is determined at fertilization by zygotic sex chromosome composition. In other species, including all crocodilians, most turtles and some lizards, sex is determined by temperature during the earlier stages of gonadal differentiation. The effects of exogenous estrogens, antiestrogens and aromatase inhibitors at different temperatures have unambiguously demonstrated the involvement of estrogens in sexual differentiation of the gonads. Aromatase is the enzyme that converts androgens to estrogens. Gonadal aromatase activity is well correlated with gonadal structure. (...) It increases exponentially in differentiating ovaries, whereas it remains low in differentiating testes. Moreover, there is a high correlation between the thermosensitive periods for both ovary differentiation and increase in aromatase activity. We suggest that a thermosensitive factor intervenes, directly or indirectly, in the transcriptional regulation of the aromatase gene in reptiles with temperature‐dependent sex determination. (shrink)

Different animal groups exhibit a surprisingly diversity of sex determination systems. Moreover, even systems that are superficially similar may utilize different underlying mechanisms. This diversity is illustrated by a comparison of sex determination in three well‐studied model organisms: the fruitfly Drosophila melanogaster, the nematode Caenorhabditis elegans, and the mouse. All three animals exhibit male heterogamety, extensive sexual dimorphism and sex chromosome dosage compensation, yet the molecular and cellular processes involved are now known to be quite unrelated. The similarities (...) must have arisen by convergent evolution. Studies of sex determination demonstrate that evolution can produce a variety of solutions to the same basic problems in development. (shrink)

Analysis of the mechanisms underlying sex determination and sex differentiation in Drosophila has provided evidence for a complex but comprehensible regulatory hierarchy governing these developmental decisions. It is suggested here that the pattern of sexual differentiation and dosage compensation characteristic of the male is a default regulatory state. Recent results have provided, in addition, some surprising and intriguing conclusions: (1) that several of the critical controlling genes produce more transcripts than was predicted from the genetic analyses; (2) that setting (...) of the alternative sex‐specific states of the doublesex (dsx) locus involves differential transcript processing; and (3) that some aspects of sexual differentation require the prolonged action of certain elements of the regulatory hierarchy. These findings are discussed in connection with the current model of sex determination in Drosophila. (shrink)

Sex is determined by non‐Mendelian genetic elements overriding the sex factors carried by the heterochromosomes in some species of terrestrial isopods. A bacterium Wolbachia and a non‐bacterial feminizing factor (f) can both force chromosomal males of Armadillidium vulgare to become phenotypic functional females. The f factor is believed to be a genetic element derived from the Wolbachia genome that becomes inserted into the host nuclear genome. The feminizing factors can be considered to be selfish genetic elements because they bias their (...) host's sex ratio to increase their own transmission. New sex‐determining genes are selected (genes resisting the feminizing effects, or the transmission of feminizing elements) as a consequence of the conflict between these elements and the rest of the host's genome. These events drive the sex‐determining mechanisms to evolve, and may explain the polymorphism of sex factors and the poor differentiation of the heterochromosomes in isopods. (shrink)

The molecular mechanism of temperature‐dependent sex determination (TSD) is a long‐standing mystery. How is the thermal signal sensed, captured and transduced to regulate key sex genes? Although there is compelling evidence for pathways via which cells capture the temperature signal, there is no known mechanism by which cells transduce those thermal signals to affect gene expression. Here we propose a novel hypothesis we call 3D‐TSD (the three dimensions of thermolabile sex determination). We postulate that the genome has capacity (...) to remodel in response to temperature by changing 3D chromatin conformation, perhaps via temperature‐sensitive transcriptional condensates. This could rewire enhancer–promoter interactions to alter the expression of key sex‐determining genes. This hypothesis can accommodate monogenic or multigenic thermolabile sex‐determining systems, and could be combined with upstream thermal sensing and transduction to the epigenome to commit gonadal fate. (shrink)

Sex selection in India and China is fostered by a limiting social structure that disallows women from performing the roles that men perform, and relegates women to a lower status level. Individual parents and individual families benefit concretely from having a son born into the family, while society, and girls and women as a group, are harmed by the widespread practice of sex selection. Sex selection reinforces oppression of women and girls. Sex selection is best addressed by ameliorating the situations (...) of women and girls, increasing their autonomy, and elevating their status in society. One might argue that restricting or prohibiting abortion, prohibiting sex selection, and prohibiting sex determination would eliminate sex selective abortion. But this decreases women's autonomy rather than increases it. Such practices will turn underground. Sex selective infanticide, and slower death by long term neglect, could increase. If abortion is restricted, the burden is placed on women seeking abortions to show that they have a legally acceptable or legitimate reason for a desired abortion, and this seriously limits women's autonomy. Instead of restricting abortion, banning sex selection, and sex determination, it is better to address the practice of sex selection by elevating the status of women and empowering women so that giving birth to a girl is a real and positive option, instead of a detriment to the parents and family as it is currently. But, if a ban on sex selective abortion or a ban on sex determination is indeed instituted, then wider social change promoting women's status in society should be instituted simultaneously. (shrink)

In 2035 global egg demand will have risen 50% from 1985. Because we are not able to tell in the egg whether it will become a male or female chick, billons of one day-old male chicks will be killed. International research initiatives are underway in this area, and governments encourage the development of an alternative with the goal of eliminating the culling of day-old male chicks. The Netherlands holds an exceptional position in the European egg trade, but is also the (...) only country in the European Union where the downside of the egg sector, the practice of killing day-old male chicks, is a recurrent subject of societal debate. ‘Preventing the killing of young animals’ and ‘in ovo sex determination’ are the two alternative approaches available to solve this problem. It is clear that both approaches solve the problem of killing day-old male chicks, either by keeping them alive or by preventing them from living, but they also raise a lot of new animal welfare-related dilemmas. A thorough analysis was undertaken of these dilemmas and the results are presented in this article. The analysis resulted in an ethical framework based on the two main approaches in bioethics: a consequentialist approach and a deontological approach. This ethical framework was used to develop an online survey administered to ascertain Dutch public opinion about these alternative approaches. The results show that neither alternative will be fully accepted, or accepted by more than half of Dutch society. However, the survey does provide an insight into the motives that are important for people’s choice: food safety and a good treatment of animals. Irrespective of the approach chosen, these values should be safeguarded and communicated clearly. (shrink)

In Caenorhabditis elegans, sex is determined by the number of X chromosomes which, in turn, determines the expression of the X‐linked gene xol‐1. Recent work(1) has shown that xol‐1 expression is controlled by least two distinct regulatory mechanisms, one transcriptional and another post‐transcriptional. The transcriptional regulator is a repressor acting in XX embryos; although the specific gene has not been identified, the chromosome region has been defined. A previously defined regulator of xol‐1, known as fox‐1, maps to a different region (...) of the X chromosome and works post‐transcriptionally, consistent with the identification of the fox‐1 gene product as a putative RNA binding protein(2). (shrink)

The endangered species Tokudaia osimensis has the unique chromosome constitution of 2n = 25, with an XO/XO sex chromosome configuration (2n = 25; XO). There is urgency to preserve this species and to elucidate the regulator(s) that can discriminate the males and females arising from the indistinguishable sex chromosome constitution. However, it is not realistic to examine this rare animal species by sacrificing individuals. Recently, true naïve induced pluripotent stem cells were successfully generated from a female T. osimensis, and the (...) sexual plasticity of its germ cells was elucidated. This achievement constitutes the basis of an attractive research area, including embryonic fate determination, sex determination, and factor(s) that can replace the Y chromosome. In this essay, concrete strategies to conserve rare animal species and to reveal their specific characteristics using other compatible and abundant animals are proposed. -/- . (shrink)

Corporations play a historic role in generating wealth but sometimes have a contentious impact on the environment and society as a whole. In recent years, corporations have become more sensitive to social issues and stakeholder concerns, and are collectively striving to become better corporate citizens. Business schools must prepare their graduates for success within these organizations by ensuring they are exposed to the best practices for implementing corporate sustainability initiatives and for measuring the social and financial impacts of these activities. (...) This article provides implications for curriculum by examining recent editions of Corporate Finance/Financial Management and Financial and Managerial Accounting textbooks commonly used by undergraduate students in North America to see how much space is devoted to these topics. The study finds that Cost/Managerial Accounting textbooks have the highest coverage related to sustainability and environmental topics. (shrink)

A hypothesis on the evolutionary origin of the genetic pathway of sex determination in the nematode Caenorhabditis elegans is presented here. It is suggested that the pathway arose in steps, driven by frequency‐dependent selection for the minority sex at each step, and involving the sequential acquisition of dominant negative, neomorphic genetic switches, each one reversing the action of the previous one. A central implication is that the genetic pathway evolved in reverse order from the final step in the hierarchy (...) up to the first. The possible applicability of the model to the other well‐characterized sex determination pathway, that of Drosophila melanogaster, and to sex determination in mammals, is discussed, along with some potential implications for pathway evolution in general. Finally, the specific molecular and population genetic questions that the model raises are described and some tests are proposed. (shrink)

Maize develops separate male and female flowers in different locations on a single plant. Male flowers develop at the tip of the shoot in the tassel, and female flowers develop on the ears, which terminate short branches. The development of male flowers in tassels and female flowers in ears is the result of selective abortion of pistils or stamens, respectively, in developing florets. Genetic analysis has shown that stamen abortion and pistil abortion are under the control of two different genetic (...) pathways. Local levels of the plant hormone gibberellic acid determine whether or not stamens are suppressed. Pistil abortion is under the regulation of the tassel seed genes, one of which has been shown to encode a short‐chain alcohol dehydrogenase. The tassel seed genes play a role in regulating the fate of inflorescence meristems as well as pistil primordium fate. (shrink)

Our goal in this paper is to reassess the relationship between norms and life by drawing on the philosophy of Georges Canguilhem, particularly some of his unpublished lectures about teratology and sexual determination. First, we discuss the difficulties Canguilhem identified in the introduction of life and sexuality as objects of philosophical reflection. Second, we reassess Canguilhem’s understanding of normativity as rooted in life and the axiological activity of the living. Third, we analyze how Canguilhem drew from past and contemporary (...) teratology to conceive of the notions of anomaly and abnormality. Finally, we reconstruct Canguilhem’s analysis of a case of hermaphroditism, highlighting how he presented it as evidence that sexual determination is the result of a normative choice. One of the key contributions of the paper to scholarly literature on Canguilhem is a better understanding of his notion of choice, which was considered not the conscious and intentional act of a subject but rather an axiological activity of the living. We conclude by positioning Canguilhem’s concept of normativity and his belief that norms are produced by the living in relation to the naturalist/normativist divide in medicine. (shrink)

Sex determination in most organisms involves a simple binary fate choice between male or female development; the outcome of this decision has profound effects on organismal biology, biochemistry and behaviour. In the nematode C. elegans, there is also a binary choice, either male or hermaphrodite. In C. elegans, distinct genetic pathways control somatic and germline sexual cell fate. Both pathways share a common set of globally acting regulatory genes; however, germline-specific regulatory genes also participate in the decision to make (...) male or female gametes. The determination of sexual fate in the germline of the facultative hermaphrodite poses a special problem, because first sperm then oocytes are produced. It has emerged that additional layers of post-transcriptional regulation have been imposed to modulate the activities of the global sex-determining genes, tra-2 and fem-3; the balance between these activities is crucial in controlling sexual cell fate in the hermaphrodite germline. BioEssays 23:596–604, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

The signal for sex determination in the nematode Caenorhabditis elegans is the ratio between the number of × chromosomes and the number of sets of autosomes (the X/A ratio). Animals with an X/A ratio of 0.67 (a triploid with two × chromosomes) or less are males. Animals with an X/A ratio of 0.75 or more are hermaphrodites. Thus, diploid males have one × chromosome and diploid hermaphrodites have two × chromosomes. However, the difference in X‐chromosome number between the sexes (...) is not reflected in general levels of X‐linked gene expression because of the phenomenon of dosage compensation. In dosage compensation, X‐linked gene expression appears to be ‘turned down’ in 2X animals to the 1X level of expression. An intriguing and unexplained finding is that mutations and X‐chromosome duplications that elevate X‐linked gene expression also feminize triploid males. One way that this relationship between sex determination and X‐linked gene expression may be operating is discussed. (shrink)