寻找人类性别决定基因的历程

动物和人类性别决定机制的探讨是生命科学中一个重要研究领域,性决定和性分化过程决定着雌性和雄性两种性别的存在。性别决定是在受精的瞬间就确定了的,是性分化的遗传基础;而性分化则是一个由早期胚胎至性成熟分化发育的复杂调控过程。该项研究不仅有益于对人类性别相关疾病的诊断治疗,而且对于动物性别的人为控制和个体性别鉴定,以及对于从低等脊椎动物到人类性别决定机制进化的探讨都具有重大价值。１　人类中存在性别决定基因对于哺乳动物的早期研究结果已使人们认识到精子有两种类型：“Ｘ精子”和“Ｙ精子”,受精时哪种类型的精…     

哺乳动物性腺分化的分子子基础

哺乳动物性腺分化的分子子基础宋平,胡珈瑞（武汉大学生命科学院,武汉４３００７２）１性别决定和分化哺乳动物性别决定和分化始于建立染色体性别时卵细胞受精的那一瞬间。有一条正常Ｙ染色体的哺乳动物为雄性,缺少Ｙ染色体的则为雌性;Ｙ染色体上含有ＳＲＹ（Ｓｅｘｄ...     

用分离精子进行性别控制研究的现状

哺乳动物后代性别控制的方法有两种,即植入前胚胎性别的选择和受精前精子的分离,后者是动物性别控制最有效的途径。目前最有重复性、科学性和有效性的分离精子的方法,是根据精子DNA含量存在差异的原理,利用荧光染料与DNA相结合,并通过流动细胞检索分离仪进行精子的分离。     

哺乳动物性别决定基因的研究进展

哺乳动物的性别发育经历了个连续不同时期;受精时期性染色体的构建（XY或XX）;性腺发育和分化（精巢或卵巢）;获得恰当的性别表现型（雄性或雌性）。人们已经发现睾丸决定因子（Testis determining factor）就是SRY（Sex determining region on Y chromosome）,并逐渐确定了其他与性别决定和性别反转相关的基因,如SOX9,DAX1,SF1,WT1,GATA-4等。综述了与哺乳动物性别控制有关的基因研究进展。     

部分水产养殖动物性别控制基因的研究进展

动物的性别是受遗传或环境等因素控制的。自从在哺乳动物中发现了性别决定基因SRY后,还发现了许多其他与性别控制和性腺发育相关的基因。由于海水养殖动物的性别控制技术在遗传育种和生产中十分重要,因此利用现代分子生物技术研究性别控制的基因成为热点。本文综述了鱼类、锯缘青蟹、海龟和海胆等水产养殖动物性别控制基因的研究进展。     

哺乳动物卵母细胞成熟和受精中细胞骨架重组和作用

卵母细胞成熟和受精是动物生殖过程的核心环节。细胞骨架是遍布于卵母细胞胞质中的一种复杂的蛋白质纤维网络,研究表明,卵母细胞成熟和受精过程中伴随着广泛的胞质骨架重组。哺乳动物卵母细胞和早期胚胎中细胞骨架具有其独特的分布和功能,使卵母细胞和胚胎呈现出不同的变化特点。微丝、微管的分布变化与卵母细胞成熟和受精中遗传物质的重组密切相关。近年来,对哺乳动物不同物种间卵母细胞和胚胎中细胞骨架成分的研究取得了很大的进展,结合这些研究成果,对哺乳动物卵母细胞成熟和受精过程中细胞骨架的重组、分布和作用进行了介绍。同时,对多种信号转导途径参与卵母细胞成熟和受精中细胞骨架系统的调控也作了探讨。     

受精的生物学及化学

一个多世纪以来科学家们一直对“受精”给予极大的关注。近年来由于扩大了对哺乳动物受精的生物学及化学的认识,因而对受精及节制生育的医学及伦理学方面均有影响。本文将叙述哺乳动物受精的细胞和分子特征,以及从精子与卵的最初相遇到形成受精卵的过程。尽管大多数论述是从体外小鼠配子实验中得出的,但是也适用于大多数哺乳动物(包括人类)体内受精过程。     

ADAMs与哺乳动物受精

ADAMs是近几年发现的一类具有多个结构区和广泛生物学功能的糖蛋白,它们在哺乳动物受精中的作用日益得到实验结果的支持,本文简要总结了近几年ADAMs在哺乳动物受精中作用的研究进展。     

非哺乳类脊椎动物性别决定的研究进展

比较了非哺乳类脊椎动物和哺乳动物性别决定的差异,从影响非哺乳类脊椎动物性别决定的环境因子及其机制两方面回顾了性别决定的研究进展,分析环境因素和类固醇激素在性别决定中的作用,指出了非哺乳类脊椎动物性别决定研究中需要进一步探讨的问题。     

ADAMs与哺乳动物受精

ADAMs是近几年发现的一类具有多个结构区和广泛生物学功能的糖蛋白,它们在哺乳动物受精中的作用日益得到实验结果的支持,本文简要总结了近几年ADAMs在哺乳动物受精中作用的研究进展。     

Maternal Condition Does Not Influence Birth Sex Ratios in Anubis Baboons (Papio anubis)

Trivers and Willard predicted that when parental condition has differential effects on the fitness of male and female offspring, parents who are in good condition will bias investment toward the sex that benefits most from additional investment. Efforts to test predictions derived from Trivers and Willard''s model have had mixed results, perhaps because most studies have relied on proxy measures of parental condition, such as dominance rank. Here, we examine the effects of female baboons condition on birth sex ratios and post-natal investment, based on visual assessments of maternal body condition. We find that local environmental conditions have significant effects on female condition, but maternal condition at conception has no consistent relationship with birth sex ratios. Mothers who are in poorer condition at the time of conception resume cycling significantly later than females who are in better condition, but the sex of their infants has no effect on the time to resumption of cycling. Thus, our findings provide strong evidence that maternal condition influences females'' ability to reproduce, but females do not facultatively adjust the sex ratio of their offspring in relation to their dominance rank or current condition.     

Determinants of the sex ratio at birth: review of recent literature

The fact that more boys are born than girls (104-107 boys for every 100 girls) has been known since 1662. Factors determining the sex ratio at birth rate are of 2 kinds: factors determining the primary sex ratio, i.e., sex ratio at conception, and factors determining the survival of the embryo in utero. Y-bearing and X-bearing sperm may have different motility or different survival time. The age of the ovum at fertilization and the chemical balance of the female genital tract have an effect on sex ratio at conception. High levels of circulating gonadotropins may imply a lower sex ratio at birth as well as a higher rate of dizygotic twinning. Male conception also appears to be higher early and late in the menstrual cycle. The fact that women exposed to higher coital rates conceive earlier in the menstrual cycle may account for the greater number of boys born during wars. Prenatal male mortality is reportedly highest between gestational months 3-5, lower between months 6-8, and higher again st term. Also, immunological interaction between mother and embryo may account for some sex selective spontaneous abortions. 3 sociodemographic determinants of sex ratio at birth are thought to be maternal age, paternal age, and birth order. Higher prenatal male mortality may be correlated with socioeconomic conditions, since higher socioeconomic status lowers prenatal mortality in general. The effects of parental age, birth order, and parity are less clear. Race is also a factor, since the sex ratio at birth for blacks is lower (102-104) than for whites (106). 14 univariate and 19 multivariate studies of effects of maternal age, paternal age, parity, birth order, race, and socioeconomic status on sex ratio at birth, with sample sizes in the millions from various countries have been analyzed. More boys are born to younger parents, and lower order births have a higher proportion of males than do higher order births. In the multivariate analyses, when the effects of paternal and and birth order are controlled for, the effect of maternal age weakens, and the effect of paternal age appears to be stronger. The effect of birth order remains but is very small, and the effect of race persists independent of any effect of other variables. Maternal age, parity, and birth order are positively correlated with proportion of male stillbirths. The results of the multivariate analyses show all of the effects to be very small, but that maternal age has no effect on sex ratio at birth; paternal age and birth order have a negative effect, and the racial effect persists independent of any other effect. The racial effect is clearly biologically determined at conception because blacks have higher levels of circulating gonadotropin and therefore a higher probability of conceiving girls. Parents in higher socioeconomic classes are more likely to have sons, but the effect is largely due to the excess male mortality during most of the gestational period.     

Offspring sex ratio skew in the sexually monomorphic house martin Delichon urbicum

Sex ratio at conception may be under selection pressure, given that male and female offspring differ in the cost of production or generate different fitness returns under specific conditions. We studied adjustments in the primary, secondary and tertiary sex ratio in house martin Delichon urbicum, which is a sexually monomorphic, socially monogamous, colonial bird. Males of this species engage in extra‐pair copulations with heavy males acquiring the highest fertilization success. We analyzed variation in the sex ratio in relation to clutch size and parental characteristics including body condition, wing length, as well as length and pigmentation of the white rump patch during three breeding seasons. The only variable which significantly explained the variation in the sex ratio was wing length of the social father and mother. The proportion of sons among offspring was positively correlated to wing length of the social father and negatively correlated to mother wing length. Social father wing length positively correlated with mean brood body mass at fledging, which may suggest that females that mated with long‐winged males produced sons, which acquired the highest total fertilization success. Consequently, our results indicate that house martin females may adaptively adjust offspring sex composition at egg laying in relation to the characteristics of their social mate.     

Sex ratio at birth and mortality rates are negatively related in humans

Evolutionary theory posits that resource availability and parental investment ability could signal offspring sex selection, in order to maximize reproductive returns. Non-human studies have provided evidence for this phenomenon, and maternal condition around the time of conception has been identified as most important factor that influence offspring sex selection. However, studies on humans have reported inconsistent results, mostly due to use of disparate measures as indicators of maternal condition. In the present study, the cross-cultural differences in human natal sex ratio were analyzed with respect to indirect measures of condition namely, life expectancy and mortality rate. Multiple regression modeling suggested that mortality rates have distinct predictive power independent of cross-cultural differences in fertility, wealth and latitude that were earlier shown to predict sex ratio at birth. These findings suggest that sex ratio variation in humans may relate to differences in parental and environmental conditions.     

The variations of human sex ratio at birth with time of conception within the cycle, coital rate around the time of conception, duration of time taken to achieve conception, and duration of gestation: a synthesis

There is a large research literature on the variation of human sex ratio (proportion of males at birth) with (1) time of insemination within the mother's fruitful cycle (TWC), (2) duration of gestation (DOG), (3) coital frequency, here called ‘coital rate’ (CR) and (4) duration of time taken to achieve conception in a period of risk (viz. in the absence of birth limitation methods) (TTC). The variation of sex ratio with each of these four variables has usually been treated as a discrete topic. Consider the four propositions that each of these sorts of variation exists. Here it is argued that these propositions entail one another to varying degrees, and that, for that reason, empirical failures to detect (at conventional levels of significance) one such form of variation (as e.g. with time to conception) should not justify rejecting the hypothesis that such variation exists until the whole network of propositions has been considered. Evidence that offspring sex ratio varies with time of conception within the cycle is strong. It is argued here that, as a consequence, the available data constitute evidence that sex ratio varies with CR and with time to achieve conception, although this variation is small, difficult to detect and of no clinical significance. Lastly, sex ratio varies substantially with DOG, though the explanation for this is not established: it is suggested that the present treatment provides a testable framework for such an explanation.     

Genetic Control of Spermatogenesis and Sex Determination in Mammals

The material was analyzed on the main problems of genetics of mammalian spermatogenesis, sex determination, its reversion and other defects from the standpoint of current cytological and molecular-genetic concepts of functional activity of the parental genomes after fertilization and behavior of their chromosomes at the early embryonic stages. On the basis of this analysis, a hypothesis has been proposed, which explains a high percentage (50% or more) of early embryonic mortality in placental mammals under the conditions of natural and extracorporeal fertilization, as well as regular appearance of defects in the course of natural sex determination, including the appearance of representatives of both sex minorities. We do not make pretense to comprehensive and deep analysis of male gametogenesis and sex determination in mammals.     

Genetic control of spermatogenesis and sex determination in mammals

The material was analyzed on the main problems of genetics of mammalian spermatogenesis, sex determination, its reversion and other defects from the standpoint of current cytological and molecular-genetic concepts of functional activity of the parental genomes after fertilization and behavior of their chromosomes at the early embroyonic stages. On the basis of this analysis, a hypothesis has been proposed, which explains a high percentage (50% or more) of early embryonic mortality in placental mammals under the conditions of natural and extracorporeal fertilization, as well as regular appearance of defects in the course of natural sex determination, including the appearance of representatives of both sex minorities. We do not make pretense to comprehensive and deep analysis of male gametogenesis and sex determination in mammals.     

Extreme sex ratio variation in relation to change in condition around conception

Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. Studies investigating sex ratio variation in mammals have produced notoriously inconsistent results, although recent studies suggest more consistency if sex ratio variation is related to maternal condition at conception, potentially mediated by changes in circulating glucose level. Consequently, we hypothesized that change in condition might better predict sex ratio variation than condition per se. Here, we investigate sex ratio variation in feral horses (Equus caballus), where sex ratio variation was previously shown to be related to maternal condition at conception. We used condition measures before and after conception to measure the change in condition around conception in individual mothers. The relationship with sex ratio was substantially more extreme than previously reported: 3% of females losing condition gave birth to a son, whereas 80% of those females that were gaining condition gave birth to a son. Change in condition is more predictive of sex ratio than actual condition, supporting previous studies, and shows the most extreme variation in mammals ever reported.     

Effect of timing of artificial insemination on sex ratio

For a number of years, the time of insemination or mating during estrus has been believed to influence the sex ratio of offspring, with early insemination resulting in more females and late insemination, more males. Possible mechanisms of altering the sex ratio include facilitating or inhibiting the transport of either X- or Y-chromosome-bearing sperm through the reproductive tract, preferential selection of sperm at fertilization, or sex-specific death of embryos after fertilization. In livestock species, there is evidence for preferential selection of X- or Y-bearing sperm, based on the maturational state of the oocyte at fertilization. In deer and sheep, early and late insemination appears to skew the sex ratio toward females and males, respectively. In cattle, conflicting reports on the effect of time of insemination on sex ratio make the premise less clear. Many of the published studies lack adequate observations for definitive conclusions and/or are based on infrequent observations of estrus, making it difficult to assess the effect of time of insemination on sex ratio. It is likely that any effect of time of insemination on sex ratio in cattle is relatively small. Evidence is accumulating that treatments used for synchronization of estrus or ovulation in cattle may influence the sex ratio.     

对亲本受孕时生理状态与子代性比关系的某些理论的检验

在亲本受孕时生理状态与代性比的关系上存在着多种理论。在１９８８－１９９２年期间，作者用实验对其中的营养理论、氧化还原理论、酸碱理论和激素假说的部分观点进行了检验。结果表明：这些理论在某种速度上均具有合理性。作者还发现：这些理论之间是相互联系的。用一系列生理指标来描述双亲受孕时影响子代性比的生理状态，对于通过调节配种时双亲的生理状态来控制子代性比具有重要意义。