共查询到20条相似文献,搜索用时 33 毫秒
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Eggert C 《Reproduction, nutrition, development》2004,44(6):539-549
We review and discuss current knowledge about sex determination in amphibians. The astonishing wide variety of mechanisms of genotypic sex determination is presented and discussed in an evolutionary context. We recall the natural occurrence of transitory juvenile hermaphroditism in some species. Our present knowledge of the mechanisms of sex determination in amphibians is compared to that in mammals. The influence of epigenetic factors, and especially temperature is highlighted. In amphibians, the influence of temperature on sexual differentiation, that can prevail over genotypic sex determination, remains poorly considered in publications. We suggest that studies on genetic and epigenetic factors of gonadal sex differentiation in amphibians could provide substantial information on the evolutionary process of sex determination mechanisms in current living vertebrates. 相似文献
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Schartl M 《Current opinion in genetics & development》2004,14(6):634-641
Birds, reptiles, amphibia and fish have an enormous variety of chromosomal sex determination mechanisms that apparently do not follow any phylogenetic or taxonomic scheme. A similar picture is now emerging at the molecular level. Most genes that function downstream of the mammalian master sex-determining gene, Sry, have been found in non-mammalian vertebrates. Although the components of the machinery that determines sex seem to be conserved, their interaction and most importantly the initial trigger is not the same in all vertebrates. This variety is the consequence of the extremely dynamic process of the evolution of sex determination mechanisms and sex chromosomes, which is prone to create differences rather than uniformity. 相似文献
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Martina Johnson Pokorná Lukáš Kratochvíl 《Biological reviews of the Cambridge Philosophical Society》2016,91(1):1-12
Amniote vertebrates, the group consisting of mammals and reptiles including birds, possess various mechanisms of sex determination. Under environmental sex determination (ESD), the sex of individuals depends on the environmental conditions occurring during their development and therefore there are no sexual differences present in their genotypes. Alternatively, through the mode of genotypic sex determination (GSD), sex is determined by a sex‐specific genotype, i.e. by the combination of sex chromosomes at various stages of differentiation at conception. As well as influencing sex determination, sex‐specific parts of genomes may, and often do, develop specific reproductive or ecological roles in their bearers. Accordingly, an individual with a mismatch between phenotypic (gonadal) and genotypic sex, for example an individual sex‐reversed by environmental effects, should have a lower fitness due to the lack of specialized, sex‐specific parts of their genome. In this case, evolutionary transitions from GSD to ESD should be less likely than transitions in the opposite direction. This prediction contrasts with the view that GSD was the ancestral sex‐determining mechanism for amniote vertebrates. Ancestral GSD would require several transitions from GSD to ESD associated with an independent dedifferentiation of sex chromosomes, at least in the ancestors of crocodiles, turtles, and lepidosaurs (tuataras and squamate reptiles). In this review, we argue that the alternative theory postulating ESD as ancestral in amniotes is more parsimonious and is largely concordant with the theoretical expectations and current knowledge of the phylogenetic distribution and homology of sex‐determining mechanisms. 相似文献
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Christine Grossen Samuel Neuenschwander Nicolas Perrin 《Evolution; international journal of organic evolution》2011,65(1):64-78
Sex determination is often seen as a dichotomous process: individual sex is assumed to be determined either by genetic (genotypic sex determination, GSD) or by environmental factors (environmental sex determination, ESD), most often temperature (temperature sex determination, TSD). We endorse an alternative view, which sees GSD and TSD as the ends of a continuum. Both effects interact a priori, because temperature can affect gene expression at any step along the sex‐determination cascade. We propose to define sex‐determination systems at the population‐ (rather than individual) level, via the proportion of variance in phenotypic sex stemming from genetic versus environmental factors, and we formalize this concept in a quantitative‐genetics framework. Sex is seen as a threshold trait underlain by a liability factor, and reaction norms allow modeling interactions between genotypic and temperature effects (seen as the necessary consequences of thermodynamic constraints on the underlying physiological processes). As this formalization shows, temperature changes (due to e.g., climatic changes or range expansions) are expected to provoke turnovers in sex‐ determination mechanisms, by inducing large‐scale sex reversal and thereby sex‐ratio selection for alternative sex‐determining genes. The frequency of turnovers and prevalence of homomorphic sex chromosomes in cold‐blooded vertebrates might thus directly relate to the temperature dependence in sex‐determination mechanisms. 相似文献
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《Genomics》2022,114(2):110277
Sexual reproduction is a diverse and widespread process. In gonochoristic species, the differentiation of sexes occurs through diverse mechanisms, influenced by environmental and genetic factors. In most vertebrates, a master-switch gene is responsible for triggering a sex determination network. However, only a few genes have acquired master-switch functions, and this process is associated with the evolution of sex-chromosomes, which have a significant influence in evolution. Additionally, their highly repetitive regions impose challenges for high-quality sequencing, even using high-throughput, state-of-the-art techniques. Here, we review the mechanisms involved in sex determination and their role in the evolution of species, particularly vertebrates, focusing on sex chromosomes and the challenges involved in sequencing these genomic elements. We also address the improvements provided by the growth of sequencing projects, by generating a massive number of near-gapless, telomere-to-telomere, chromosome-level, phased assemblies, increasing the number and quality of sex-chromosome sequences available for further studies. 相似文献
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早期胚胎的发育选择:性别决定 总被引:2,自引:0,他引:2
性别决定是一个复杂的发育调控过程, 早期胚胎发育过程中, 雌雄二者必居其一的发育选择是胚胎性腺形成必须的发育决定。文章综述了动物性别决定的遗传系统、性腺发生、性别决定关键基因及其作用机制, 从分子进化的角度分析了性染色体与性别决定形成机制, 提示性别决定基因在进化中总是趋向异配性染色体。 相似文献
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M Steinmann-Zwicky 《BioEssays : news and reviews in molecular, cellular and developmental biology》1992,14(8):513-518
Sex determination in the germ line may either rely on cell-autonomous genetic information, or it may be imposed during development by inductive somatic signals. In Drosophila, both mechanisms contribute to ensure that germ cells are oogenic when differentiating in females and spermatogenic when differentiating in males. Some of the genes that are involved in germ line sex determination have been identified. In other species, including vertebrates, inductive signals are commonly used to determine the sex of germ cells. 相似文献
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Mizuno S Kunita R Nakabayashi O Kuroda Y Arai N Harata M Ogawa A Itoh Y Teranishi M Hori T 《Cytogenetic and genome research》2002,99(1-4):236-244
Since the discovery of SRY/SRY as a testis-determining gene on the mammalian Y chromosome in 1990, extensive studies have been carried out on the immediate target of SRY/SRY and genes functioning in the course of testis development. Comparative studies in non-mammalian vertebrates including birds have failed to find a gene equivalent to SRY/SRY, whereas they have suggested that most of the downstream factors found in mammals including SOX9 are also involved in the process of gonadal differentiation. Although a gene whose function is to trigger the cascade of gene expression toward gonadal differentiation has not been identified yet on either W or Z chromosomes of birds, a few interesting genes have been found recently on the sex chromosomes of chickens and their possible roles in sex determination or sex differentiation are being investigated. It is the purpose of this review to summarize the present knowledge of these sex chromosome-linked genes in chickens and to give perspectives and point out questions concerning the mechanisms of avian sex determination. 相似文献
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Alan Brelsford Matthias Stöck Caroline Betto‐Colliard Sylvain Dubey Christophe Dufresnes Hélène Jourdan‐Pineau Nicolas Rodrigues Romain Savary Roberto Sermier Nicolas Perrin 《Evolution; international journal of organic evolution》2013,67(8):2434-2440
Comparative genomic studies are revealing that, in sharp contrast with the strong stability found in birds and mammals, sex determination mechanisms are surprisingly labile in cold‐blooded vertebrates, with frequent transitions between different pairs of sex chromosomes. It was recently suggested that, in context of this high turnover, some chromosome pairs might be more likely than others to be co‐opted as sex chromosomes. Empirical support, however, is still very limited. Here we show that sex‐linked markers from three highly divergent groups of anurans map to Xenopus tropicalis scaffold 1, a large part of which is homologous to the avian sex chromosome. Accordingly, the bird sex determination gene DMRT1, known to play a key role in sex differentiation across many animal lineages, is sex linked in all three groups. Our data provide strong support for the idea that some chromosome pairs are more likely than others to be co‐opted as sex chromosomes because they harbor key genes from the sex determination pathway. 相似文献
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West SA Shuker DM Sheldon BC 《Evolution; international journal of organic evolution》2005,59(6):1211-1228
Studies of sex allocation offer excellent opportunities for examining the constraints and limits on adaptation. A major topic of debate within this field concerns the extent to which the ability of individuals to adaptively manipulate their offspring sex ratio is determined by constraints such as the method of sex determination. We address this problem by comparing the extent of sex-ratio adjustment across taxa with different methods of sex determination, under the common selective scenario of interactions between relatives. These interactions comprise the following: local resource competition (LRC), local mate competition (LMC), and local resource enhancement (LRE). We found that: (1) species with supposedly constraining methods of sex determination showed consistent sex-ratio adjustment in the predicted direction; (2) vertebrates with chromosomal sex determination (CSD) showed less adjustment then haplodiploid invertebrates; (3) invertebrates with possibly constraining sex-determination mechanisms (CSD and pseudo-arrhenotoky) did not show less adjustment then haplodiploid invertebrates; (4) greater sex-ratio adjustment was seen in response to LRC and LMC than LRE; (5) greater sex-ratio adjustment was seen in response to interactions between relatives (LRC, LMC, and LRE) compared to responses to other environmental factors. Our results also illustrate the problem that sex-determination mechanism and selective pressure are confounded across taxa because vertebrates with CSD are influenced primarily by LRE whereas invertebrates are influenced by LRC and LMC. Overall, our analyses suggest that sex-allocation theory needs to consider simultaneously the influence of variable selection pressures and variable constraints when applying general theory to specific cases. 相似文献
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Matsuda M 《Development, growth & differentiation》2003,45(5-6):397-403
Although sex determination systems in animals are diverse, sex-determining genes have been identified only in mammals and some invertebrates. Recently, DMY (DM domain gene on the Y chromosome) has been found in the sex-determining region on the Y chromosome of the teleost medaka fish, Oryzias latipes. Functional and expression analyses of DMY show it to be the leading candidate for the male-determining master gene of the medaka. Although some work is required to define DMY as the master sex-determining gene, medaka is expected to be a good experimental animal for investigating the precise mechanisms involved in primary sex determination in non-mammalian vertebrates. In this article, the process of identification of DMY and is summarized and the origins of DMY and sexual development of the medaka's gonads are reviewed. In addition, putative functions of DMY are discussed. 相似文献
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Mateus Contar Adolfi Peter Fischer Amaury Herpin Martina Regensburger Mariko Kikuchi Minoru Tanaka Manfred Schartl 《Molecular reproduction and development》2019,86(10):1405-1417
In vertebrates, there is accumulating evidence that environmental factors as triggers for sex determination and genetic sex determination are not two opposing alternatives but that a continuum of mechanisms bridge those extremes. One prominent example is the model fish species Oryzias latipes which has a stable XX/XY genetic sex determination system, but still responds to environmental cues, where high temperatures lead to female‐to‐male sex reversal. However, the mechanisms behind are still unknown. We show that high temperatures increase primordial germ cells (PGC) numbers before they reach the genital ridge, which, in turn, regulates the germ cell proliferation. Complete ablation of PGCs led to XX males with germ cell less testis, whereas experimentally increased PGC numbers did not reverse XY genotypes to female. For the underlying molecular mechanism, we provide support for the explanation that activation of the dmrt1a gene by cortisol during early development of XX embryos enables this autosomal gene to take over the role of the male determining Y‐chromosomal dmrt1bY. 相似文献
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Rajkumar S. Radder 《Journal of biosciences》2007,32(2):1213-1220
During the past decade, maternally derived steroid hormones in the egg yolk of oviparous vertebrates have been the focus of attention for their possible role in sex determination and hence, information on the consequences of maternal egg yolk steroids on sex determination has accumulated rapidly in reptiles and birds. Until recently, the observations were dominated by the idea that yolk steroids of maternal origin play an important role in sex determination of oviparous vertebrates. However, more recent studies have cast significant doubt on the above conclusion. These studies suggest instead that steroids may be present in the yolk simply as the byproduct of passive uptake during yolk formation or observed correlations might reflect embryonically produced rather than maternally derived steroids. Thus, the objective of the present review is (i) to provide an overview of such paradoxical observations on the role of maternal yolk steroids in sex determination of reptiles, (ii) to identify and provide brief explanations for the observed paradoxical results, and (iii) to provide some future research directions. 相似文献
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Temperature-related birth sex ratio bias in historical Sami: warm years bring more sons 总被引:1,自引:0,他引:1
The birth sex ratio of vertebrates with chromosomal sex determination has been shown to respond to environmental variability, such as temperature. However, in humans the few previous studies on environmental temperature and birth sex ratios have produced mixed results. We examined whether reconstructed annual mean temperatures were associated with annual offspring sex ratio at birth in the eighteenth to nineteenth century Sami from northern Finland. We found that warm years correlated with a male-biased sex ratio, whereas a warm previous year skewed sex ratio towards females. The net effect of one degree Celsius increase in mean temperature during these 2 years corresponded to approximately 1% more sons born annually. Although the physiological and ecological mechanisms mediating these effects and their evolutionary consequences on parental fitness remain unknown, our results show that environmental temperature may affect human birth sex ratio. 相似文献
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Valleley EM Cartwright EJ Croft NJ Markham AF Coletta PL 《The Journal of experimental zoology》2001,291(1):85-91
Since the discovery of the sex-determining gene, Sry, a number of genes have been identified which are involved in sex determination and gonadogenesis in mammals. Although Sry is known to be the testis-determining factor in mammals, this is not the case in non-mammalian vertebrates. Sox9 is another gene that has been shown to have a male-specific role in sex determination, but, unlike Sry, Sox9 has been shown to be involved in sex determination in mammals, birds, and reptiles. This is the first gene to be described that has a conserved role in sex determination in species with either chromosomal or environmental sex-determining mechanisms. Many reptiles do not have sex chromosomes but exhibit temperature-dependent sex determination (TSD). Sox9 has been shown to be expressed in both turtle and alligator during gonadogenesis. To determine if Sox9 also has a role in a gecko species with TSD, we studied gonadal expression of Sox9 during embryonic development of the Leopard gecko (Eublepharis macularius). Gecko Sox9 was found to be highly conserved at the nucleotide level when compared to other vertebrate species including human, chick, alligator, and turtle. Sox9 was found to be expressed in embryos incubated at the male-producing temperature (32.5 degrees C) as well as in embryos incubated at the female-producing temperatures (26 and 34 degrees C), Northern blot analysis showed that Sox9 was expressed at both temperatures from morphological stages 31 to 37. mRNA in situ hybridisation on isolated urogenital systems showed expression at both female- and male-producing temperatures up to stage 36. After this stage, no expression was seen in the female gonads but expression remained in the male. These data provide further evidence that Sox9 is an essential component of a testis-determining pathway that is conserved in species with differing sex-determining mechanisms. 相似文献