Sex determination and differentiation in organisms other than higher plants

The understanding of sex determination in general, but in particular in mammals, has been a subject of scientific speculation for a long time. It has been shown that in many vertebrate and invertebrate species, the sex of an individual is determined by the individual's chromosomal constitution. Initial studies of classical genetic searching for sex-transforming mutations and the scrupulous analyses of modified phenotypes have shed light on the mechanism(s) of sex-determination. They paved the road to successful studies at molecular level. After a brief review on sex determination in chosen model species, the “Drosophila system” is presented to exemplify a possible general principle for sex determinism.     

Sex determination in Drosophila melanogaster: X-linked genes involved in the initial step of Sex-lethal activation

Sex determination is the commitment of an embryo to either the female or the male developmental pathway. The ratio of X chromosomes to sets of autosomes is the primary genetic signal that determines sex in Drosophila, by triggering the functional state of the gene Sex-lethal: in females (2X;2A) Sxl will be ON, whereas in males (X;2A) Sxl will be OFF. Genetic and molecuar studies have defined a set of genes involved in the formation of the X:A signal, as well as other genes, with either maternal or zygotic effects, which are also involved in regulating the initial step of Sex-lethal activation. We review these data and present new data on two more regions of the X chromosome that define other genes needed for Sxl activation. In addition, we report on the interaction between some of the genes regulating Sxl activation. © 1994 Wiley-Liss, Inc.     

Equine fetal sex determination using circulating cell-free fetal DNA (ccffDNA)

In this study, polymerase chain reaction (PCR) reamplification of the first PCR product (2nd-PCR) and a qPCR assay were used to detect the sex determining region Y (SRY) gene from circulating cell-free fetal DNA (ccffDNA) in blood plasma of pregnant mares to determine fetal sex. The ccffDNA was isolated from plasma of 20 Thoroughbred mares (5-13 y old) in the final 3 mo of pregnancy (fetal sex was verified after foaling). For controls, plasma from two non-pregnant mares and two virgin mares were used, in addition to the non-template control. The 182 bp nucleotide sequence corresponding to the SRY-PCR product was confirmed by DNA sequencing. Based on SRY/PCR, 8 of 11 male and 9 of 9 female fetuses were correctly identified, resulting in a sensitivity of 72.7% (for male fetuses) and an overall accuracy of 85%. Furthermore, using SRY/2nd-PCR and qPCR techniques, sensitivity and accuracy were 90.9 and 95%, respectively. In conclusion, this study is apparently the first report of fetal sex determination in mares using ccffDNA.     

Sex determination in fish: Lessons from the sex-determining gene of the teleost medaka, Oryzias latipes

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.     

Sex ratio selection and multi-factorial sex determination in the housefly: a dynamic model

Sex determining (SD) mechanisms are highly variable between different taxonomic groups and appear to change relatively quickly during evolution. Sex ratio selection could be a dominant force causing such changes. We investigate theoretically the effect of sex ratio selection on the dynamics of a multi-factorial SD system. The system considered resembles the naturally occurring three-locus system of the housefly, which allows for male heterogamety, female heterogamety and a variety of other mechanisms. Sex ratio selection is modelled by assuming cost differences in the production of sons and daughters, a scenario leading to a strong sex ratio bias in the absence of constraints imposed by the mechanism of sex determination. We show that, despite of the presumed flexibility of the SD system considered, equilibrium sex ratios never deviate strongly from 1 : 1. Even if daughters are very costly, a male-biased sex ratio can never evolve. If sons are more costly, sex ratio can be slightly female biased but even in case of large cost differences the bias is very small (<10% from 1 : 1). Sex ratio selection can lead to a shift in the SD mechanism, but cannot be the sole cause of complete switches from one SD system to another. In fact, more than one locus remains polymorphic at equilibrium. We discuss our results in the context of evolution of the variable SD mechanism found in natural housefly populations.     

Wolbachia对赤眼蜂的性别调控机制及生理影响

沃尔巴克氏体(Wolbachia)是广泛分布于节肢动物生殖组织内的一类共生细菌。它们通过共生诱导宿主赤眼蜂的产雌孤雌生殖,在生物防治上具有重要意义。文章概述了Wolbachia在赤眼蜂中的分布状况,对赤眼蜂的性别调控机制,在赤眼蜂种群中的传播及限制因素,以及对赤眼蜂适合度的影响。     

Sex ratio variance and the maintenance of environmental sex determination

Although variation in population sex ratios is predicted to increase the extinction rate of clades with environmental sex determination (ESD), ESD is still seen in a wide array of natural systems. It is unclear how this common sex-determining system has persisted despite this inherent disadvantage associated with ESD. We use simulation modelling to examine the effect of the sex ratio variance caused by ESD on population colonization and establishment. We find that an accelerating function of establishment success on initial population sex ratio favours a system that produces variance in sex ratios over one that consistently produces even sex ratios. This sex ratio variance causes ESD to be favoured over genetic sex determination, even when the mean global sex ratio under both sex-determining systems is the same. Data from ESD populations suggest that the increase in population establishment can more than offset the increased risk of extinction associated with temporal fluctuations in the sex ratio. These findings demonstrate that selection in natural systems can favour increased variance in a trait, irrespective of the mean trait value. Our results indicate that sex ratio variation may provide an advantage to species with ESD, and may help explain the widespread existence of this sex-determining system.     

Sex determination of ancient human skeletons using DNA

A method for determining the sex of human skeletons was developed using molecular genetic techniques. The amelogenin gene, found on the X and Y chromosomes, was examined using the polymerase chain reaction (PCR) and a nonradioactive dot blot procedure. DNA was analyzed from 20 modern individuals of known sex and 20 skeletons from an archaeological site in central Illinois dating to A.D. 1300. An independent assessment of the sex of each skeleton was made according to standard osteological methods. The sex of 19 ancient and 20 modern individuals was accurately determined using this molecular genetic technique. Molecular sex determination will be especially useful for juvenile and fragmentary remains when it is difficult, or impossible, to establish an individual's sex from morphological features. © 1996 Wiley-Liss, Inc.     

蜜蜂性别决定与性比调控机理研究

叙述了 4个主要蜜蜂性别决定机理的假说 :即性位点假说、基因平衡假说、蜜蜂性别决定综合假说和性基因数量决定假说。然后就蜜蜂性比由蜂王操纵 ,或是由工蜂操纵进行了论述 ,并对蜜蜂性比调控机理研究提出了一些建议     

樱桃新害虫黑腹果蝇的生物学特性

果蝇是近几年发现危害樱桃果实的一类重要害虫,在国内外樱桃产区均有发生。天水地区危害甜樱桃的果蝇有3个种,分别是黑腹果蝇Drosophila melanogaster Meigen、铃木氏果蝇Drosophila suzukii(Matsumura)和海德氏果蝇Drosophila hydei(Sturtevant),黑腹果蝇为优势种。作者记述黑腹果蝇对甜樱桃果实的危害情况、寄主范围及其生活史、生活习性、发育历期与温度的关系等,调查发现蚂蚁是樱桃果蝇的天敌之一。     

番木瓜性别决定及其鉴定研究新进展

番木瓜有3种基本性别类型,性别遗传较为复杂.就其植株的多型性表现、性别决定及其鉴定研究、连锁遗传图的构建、分子标记辅助选择技术和花器的发育等方面的研究进展进行了综述,并对番木瓜性别鉴定的应用前景做了展望.     

Sex determination in the larvae of the parasitic barnacle Heterosaccus lunatus: an experimental approach

Heterosaccus lunatus parasitizes the portunid crab, Charybdis callianassa, in Moreton bay, Queensland, Australia. With the host crabs maintained at 25 °C this sacculinid rhizocephalan released larval broods every 5-6 days. This study examines the effect of photoperiod on the sex proportions of successive larval broods of individual parasites. Parasitized host crabs were maintained individually in circulating 25 °C seawater within two light-tight boxes, each with a controlled light-dark cycle operating. Box A had an LD 16:8 cycle (summer) and Box B an LD 8:16 cycle (winter). Both boxes had five host crabs and when parasites released their larval broods the larvae were flushed out and retained in a filter. Each captured brood then had its larvae sized to determine the proportions of the two sexes present. H. lunatus is ideal for such study because the sex(es) of all the larval stages (four naupliar stages and the cyprid) can be unequivocally identified by size (length). The experiment was run over a 6-week period during March and April 2004 when a total of 86 larval broods were released and their sex proportion(s) determined. It is concluded that larval sex determination is effected by photoperiod, with females becoming dominant under the winter condition (LD 8:16) and males dominant under the summer condition (LD 16:8). All initial broods were male dominated, so for Box A broods the male preponderance was maintained, whilst for Box B broods there was the progressive changeover to female preponderance. Such environmental sex determination is unusual because it is oogenesis which is being controlled, whereby two ovum sizes can be produced, either singly or together, the larger being the male egg. Further work is now necessary to verify the likely hormonal control processes involved.     

Sex determination and sex ratio in the dioecious shrub Salix viminalis L.

 Various ecological factors (e.g. herbivory, difference between males and females in colonising ability) have been invoked to explain female-biased sex ratios in populations of willow species. It was implicitly assumed that genetic factors would lead to a balanced sex ratio in the absence of ecological disturbances. In an experiment carried out in a homogeneous environment and in the absence of herbivores the progeny sex ratio of 13 crosses of basket willow (Salix viminalis L.) was observed to range from extreme female bias to extreme male bias. The observed sex ratio cannot be explained by the presence of sex chromosomes without assuming that additional loci are also involved in the sex determination. Alternatively, the sex ratios in this study can be explained by a sex determination mechanism governed by multiple independent loci. Received: 1 February 1996 / Accepted: 14 June 1996     

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.     

Genetic sexing in Drosophila melanogaster using the alcohol dehydrogenase locus and a Y-linked translocation

Summary By incorporating ethanol (4% v/v) into the larval rearing medium of a specially constructed Drosophila melanogaster strain it was possible to produce only male adults; the female larvae died.In this strain, the male determining chromosome was linked with a positive Alcohol dehydrogenase (ADH) allele by a translocation. The females were homozygous for the null allele and hence sensitive to ethanol.This genetic sexing method is discussed in relation to its use in the genetic control of insects.     

三种模式植物性别决定的研究进展(综述)

综述白麦瓶草、玉米和黄瓜等模式植物性别决定的研究进展,并展望今后研究方向。