鱼类和两栖类性别决定的研究进展

鱼类和两栖类在脊椎动物的演化过程中是非常关键的两个类群,人们对于这两类动物性别决定的研究已经取得了一些进展.这些进展不仅对动物性别决定演化的研究有基础性贡献,而且对发展养殖业也有理论指导意义.     

甲壳动物性别分化的遗传决定及外界因素的影响

本文综述了甲壳动物的性别决定机理及外界因素对性别分化的影响,绝大多数甲壳动物没有明显的性染色体,促雄腺被认为是甲壳动物性别分化的最主要的决定因子,其作用已得到了广泛的证明,由于甲壳动物幼体在早期发育过程中具有向两性发育的潜能,促雄腺可以决定个体未来发育的性别,并且通过人为摘除或移植促雄腺的方法可以使性别已经分化的个体发生性逆转,从而改变幼体的性别。虽然甲壳动物的性别是由遗传决定的,但外界的因素经如寄生,光周期,温度或激素可以改变其性比,其中以寄生的影响研究比较多,并认为是影响某些甲壳动物性别分化的主要外界因子,由于大多数养殖的甲壳动物雌雄性之间的有体重和体长的差异在水产养殖中可以利用这些特征进行全雌全雄种苗的生产,以提高产量和效益。     

鱼类性别与性别鉴定

性别分化和性别决定相互联系又有所区别,具双向潜力的未分化性腺经过程序性发生的一系列事件,发育成精巢或卵巢,并出现第二性征的过程称为性别分化,而性别决定则是确定性分化方向的方式。       

性别决定与性染色体

较系统地介绍生物性别决定的遗传类型及其理论基础,阐明性染色体上基因的遗传特点和引起性别分化的途径;论述性别决定与性染色体的关系。     

一个新的性别决定基因DMY

虽然人们已经鉴定出了线虫、果蝇和哺乳动物的性别决定基因,但直到最近才首次在非哺乳类脊椎动物中发现了性别决定基因DMY.介绍了在青鳉中发现DMY基因的经过,发现DMY基因的意义和DMY基因在其他鱼类中的分布,最后对未来的研究进行了展望.     

鱼类性别异形和性别决定的遗传基础及其生物技术操控

鱼类养殖对世界食品特别是动物蛋白的持续供给做出了至关重要的贡献.鱼类生殖对策的多样性,特别是单性雌核生殖方式的利用已开创了鱼类遗传育种的典型范例.不少鱼类在生长和个体大小等重要经济性状上表现出显著的性别异形.性别特异分子标记的开发和性别控制生物技术的发展为增加鱼产量及其经济价值提供了重要的技术途径.随着基因组学和分子遗传学技术的迅速发展,鱼类性别异形的遗传基础逐步被揭示,鱼类性别决定机制及其性别决定相关基因的鉴定已经取得了重大进展.本文对此进行了概述,以期为该领域的深入研究提供一些方向性和目标性思考.     

甲壳动物性别分化的遗传决定及外界因素的影响(英文)

本文综述了甲壳动物的性别决定机理及外界因素对性别分化的影响。绝大多数甲壳动物没有明显的性染色体 ,促雄腺被认为是甲壳动物性别分化的最主要的决定因子 ,其作用已得到了广泛的证明。由于甲壳动物幼体在早期发育过程中具有向两性发育的潜能 ,促雄腺可以决定个体未来发育的性别 ,并且通过人为摘除或移植促雄腺的方法可以使性别已经分化的个体发生性逆转 ,从而改变幼体的性别。虽然甲壳动物的性别是由遗传决定的 ,但外界的因素比如寄生、光周期、温度或激素可以改变其性比 ,其中以寄生的影响研究比较多 ,并认为是影响某些甲壳动物性别分化的主要外界因子。由于大多数养殖的甲壳动物雌雄性之间有体重和体长的差异 ,在水产养殖中可以利用这些特征进行全雌或全雄种苗的生产 ,以提高产量和效益。     

性别决定基因

在个体发育过程中,动物的种类不同,性别决定的方式亦有差异。这取决于胚胎早期不同的性别初级信号对性别决定基因的启动和活化,活化的性别决定基因启动性别分化基因的表达,使个体的性别表现出来。本文略述与线虫、果蝇等的性别决定有关的基因。线虫(Caenorhabditis elegans)体长约1mm,雌雄同体,自体受精。有两条 X 染色体(XX);XO型线虫为雄性。线虫(C.elegans)性别决定的初级信号是 X 染色体与常染色体的比率(X∶     

植物的性别决定与伴性遗传

植物的性别决定与伴性遗传冯昌全（四川省岳池县教研室６３８３５０）动物有ＸＸ－ｘｙ型、ＺＷ－ＺＺ型等性别决定和伴性遗传的特性。那么,植物也有这些特性吗？本文就植物的性别决定和伴性遗传作一介绍,供参考。（一）植物性别的染色体决定自１９２３年发现植物性染色...     

性别决定与伴性遗传的教学

教学目的1. 以XY型性别决定为例,使学生了解雌雄异体的生物,其性别主要是由性染色体组成的差异决定的。2. 以人的红绿色盲为实例,使学生了解性染色体上基因所控制的性状与性别相关联的特殊遗传现象。3. 通过性别决定及伴性遗传的讲解,对学生进行有关性知识及近亲婚配危害的思想教育。     

Evidence of thermolabile sex determination in pejerrey*

Temperature regimes of 17 ± 1°C and 21 ±1°C early in development of pejerrey Odontesthes bonariensis produced nearly all females, whereas at 25 ± 1°C variable, sometimes male-biased sex-ratios were obtained. The critical period of thermolabile sex determination seemed to occur between 25 and 50 days post-hatch (about 11 and 21 mm s.i.) at low temperatures (17–20°C) and between 0 and 25 days (about 7 and 15 mm) at high temperatures (22–25°C). The likelihood of expression of temperature-dependent sex determination in natural populations and the possible adaptive significance of environmental sex determination in pejerrey are discussed.     

Evolutionary transitions between mechanisms of sex determination in vertebrates

Sex in many organisms is a dichotomous phenotype--individuals are either male or female. The molecular pathways underlying sex determination are governed by the genetic contribution of parents to the zygote, the environment in which the zygote develops or interaction of the two, depending on the species. Systems in which multiple interacting influences or a continuously varying influence (such as temperature) determines a dichotomous outcome have at least one threshold. We show that when sex is viewed as a threshold trait, evolution in that threshold can permit novel transitions between genotypic and temperature-dependent sex determination (TSD) and remarkably, between male (XX/XY) and female (ZZ/ZW) heterogamety. Transitions are possible without substantive genotypic innovation of novel sex-determining mutations or transpositions, so that the master sex gene and sex chromosome pair can be retained in ZW-XY transitions. We also show that evolution in the threshold can explain all observed patterns in vertebrate TSD, when coupled with evolution in embryonic survivorship limits.     

Nest-site philopatry and selection for environmental sex determination

The reason for the frequent occurrence of environmental sex determination (ESD) in reptiles is still not well understood, although much effort has been devoted to solving the issue. Stimulated by the occurrence of nest-site philopatry in some species, this paper examines a diploid model of the influence of nest-site philopatry on the evolution of ESD. Analysis shows that nest-site philopatry can lead to ESD because the fitnesses of sons and daughters are not influenced in the same way by nest-site quality. Daughters inherit the nest site and thus benefit more than sons from a high-quality nest site. Conversely, the fitness of daughters at low-quality nest sites is lower compared to the fitness of sons. Therefore, genes causing ESD can spread by causing the production of more sons at low-quality nest sites and more daughters at high-quality nest sites. Suggestions are made to test empirically whether nest-site philopatry led to the evolution of ESD. This revised version was published online in July 2006 with corrections to the Cover Date.     

Maintenance of polygenic sex determination in a fluctuating environment: an individual‐based model

R. A. Fisher predicted that individuals should invest equally in offspring of both sexes, and that the proportion of males and females produced (the primary sex ratio) should evolve towards 1:1 when unconstrained. For many species, sex determination is dependent on sex chromosomes, creating a strong tendency for balanced sex ratios, but in other cases, multiple autosomal genes interact to determine sex. In such cases, the maintenance of multiple sex‐determining alleles at multiple loci and the consequent among‐family variability in sex ratios presents a puzzle, as theory predicts that such systems should be unstable. Theory also predicts that environmental influences on sex can complicate outcomes of genetic sex determination, and that population structure may play a role. Tigriopus californicus, a copepod that lives in splash‐pool metapopulations and exhibits polygenic and environment‐dependent sex determination, presents a test case for relevant theory. We use this species as a model for parameterizing an individual‐based simulation to investigate conditions that could maintain polygenic sex determination. We find that metapopulation structure can delay the degradation of polygenic sex determination and that periods of alternating frequency‐dependent selection, imposed by seasonal fluctuations in environmental conditions, can maintain polygenic sex determination indefinitely.     

植物性别决定的研究进展

通过回顾近年来以多种植物为材料进行的性染色体观察,性别决定基因及调控方式的研究,对植物性别决定的机制进行了初步探讨,从而可以看出不同植物具有不同的性别决定机制：对于有性染色体的植物而言,目前已经从Y染色体上分离和鉴定了许多与雄性发育紧密相关的基因;部分性别决定基因和调控序列已利用构建减法文库,诱导突变体等方法从一些植物中获得。此外,还有研究表明,DNA脱甲基化,以及某些激素(如赤霉素、乙烯、Ace)都对植物的性别决定有重要作用。     

Biased sex ratios in the dioecious annual Croton texensis (Euphorbiaceae) are not due to environmental sex determination

At Arapaho Prairie, in the sandhills of western Nebraska, the dioecious annual Croton texensis (Euphorbiaceae) exhibits biased sex ratios. Moreover, the direction of bias changes from year to year: in 1994 the study population was significantly female biased, in 1995 and 1996 it was significantly male biased, and in 1997 and 1998 the sex ratio did not differ from 1 : 1. Such variation in the observed sex ratio in plants is frequently attributed to environmental sex determination (ESD), which is favored by natural selection if the rate of fitness gain across an environmental gradient is greater for one sex than the other. We performed experiments to determine: (1) whether variation in the sex ratio is correlated with environmental conditions, as would be expected if ESD is operating, and (2) whether ESD, if present, would be favored by natural selection. In a common garden experiment in which water and fertilizer were manipulated the sex ratio was marginally male biased in treatments in which water was added, but not different from 1 : 1 in other treatments. In field plots into which seeds were planted none of several soil characteristics, nor overall plot quality for C. texensis (measured as average plant biomass) were correlated with plot sex ratio. However, plots in which a large number of planted seeds emerged tended to be female biased. These results provide very weak evidence for sex ratio bias across an environmental gradient, and thus provide little evidence for ESD. Moreover, sex-by-environment interactions for fitness, which are required for the evolution of ESD, were absent for all measured variables. Thus, ESD does not appear to be favored by natural selection in this population. Instead, these biases may have been caused by differences between the sexes in germination and/or early mortality.     

膜翅目昆虫的性别决定机制

昆虫性别决定机制存在多样性和复杂性,其中膜翅目昆虫的性别决定由单双倍体决定,单倍体为雄性,二倍体为雌性。本文就膜翅目昆虫的性别决定模式和分子机制进行综述。膜翅目昆虫性别决定有6种模式,即互补性性别决定(complementary sex determination, CSD)、多位点互补性性别决定(multiple-locus CSD, ml-CSD)、基因组印记、母体效应、内共生体诱导产雌单性生殖、父本遗传基因组消除(paternal genome elimination, PGE)。其中,CSD机制是目前在膜翅目昆虫中普遍接受的性别决定模式。而蜜蜂的CSD性别决定机制是膜翅目昆虫性别决定模式中的典型代表,受csd→fem→dsx这一调控级联的控制。     

The fitness consequences of environmental sex reversal in fish: a quantitative review

Environmental sex reversal (ESR) occurs when environmental factors overpower genetic sex-determining factors. The phenomenon of ESR is observed widely in teleost species, where it can be induced by exposing developing fish to endocrine disrupting chemicals (EDCs). EDC-induced ESR has been exploited by the aquaculture industry, while ecological and evolutionary models are also beginning to elucidate the potential roles that sex-reversed individuals play in influencing population dynamics. However, how EDC exposure affects individual fitness remains relatively unknown. To date, many experimental studies have induced sex reversal in fish and measured fitness-as indicated by related traits such as size, survival and gonadal somatic index (GSI), but the reported results vary. Here, we meta-analytically combine the results of 78 studies of induced ESR to gain insight into the fitness of sex-reversed individuals. Overall, our results suggest that the fitness of fish exposed to EDCs is reduced at the time of exposure, with exposed individuals having a smaller size and likely a smaller GSI. Given a period of non-exposure, fish treated with EDCs can regain a size equal to those not exposed, although GSI remains compromised. Interestingly, survival does not appear to be affected by EDC treatment. The published reports that comprise our dataset are, however, based on captive fish and the general small size resulting from exposure is likely to lead to reduced survival in the wild. Additionally, reduced fitness-related parameters are likely to be due to exposure to EDCs rather than ESR itself. We suggest that theoretical models of ESR should account for the fitness-related effects that we report. Whilst we are able to shed light on the physical fitness of EDC-exposed fish, the behaviour of such individuals remains largely untested and should be the focus of future experimental manipulation.