人类性染色体特异ＤＮＡ对三种鱼类染色体的描绘

染色体描绘是研究基因组进化的强有力手段之一,用人Ｘ和Ｙ染色体文库特异ＤＮＡ为探针,对３种硬骨鱼类－刺鳅、黄鳝和斑马鱼的有丝分裂中期裂染色体进行了描绘研究,结果表明,在这３种鱼类的染色体组中都发现有人Ｘ染色体特DN的同源片段,它们散布在几对同源染色体中,但用人Ｙ染色体ＤＮ描绘这３种鱼类染色体时,则没有检测出可见的同源片段。同时对从低等脊椎动物到人类的Ｘ染色体进化过程进行了进一步探讨。     

人类性染色体与遗传病

人体细胞内有46条染色体,其中44条常染色体为男女共有,两条性染色体,男女有别,正常女性有两条X染色体,核型为46,XX;正常男性有一条X染色体和一条Y染色体,核型为46,XY。按人类染色体命名的国际体制,人类的46条染色体两两相配成23对,分7组,X染色体属C组,具亚中着丝粒,Y染色体属G组,有近端着丝粒。随着基因定位技术的不断发展,人们已将三千多个基因     

人类染色体着丝粒蛋白研究进展

人类染色体着丝粒蛋白研究进展朱学良（中国科学技术大学生物系合肥２３００２６）１着丝粒、动植和着丝粒一动粒复合体细胞分裂过程中姐妹染色体的均等分离是一切生物赖以生长和繁殖的基础之一。着丝粒（ｃｅｎｔｒｏｍｅｒｅ）是染色体位于初缢痕的部分,在光学显微镜下...     

白豆杉的核型和性染色体的研究

白豆杉pseudotaxus chienii(Cheng)Cheng是我国裸子植物特有属之一,雌雄异常,根尖 细胞染色体分析表明：雌株有一对异形性染色体,异配性别,属ZW型;雄株是同配性别,属ZZ型,雌株的型为2n=2x=24=22m(2SAT ZW) 2T,雄株的核型为2n=2x=24=22m(2SAT ZZ) 2T。Giemsa C-带,显示,Z染色体长短臂均具端带,W染色体不显带。     

1200条带阶段的人类染色体高分辨G带

在改良的850条带阶段的人类染色体高分辨显带技术基础上,对1200条带阶段的人类染色体高分辨G带进行了研究和识别,并按ISCN(1985)的规定对1200条带阶段的高分辨G带进行了命名和划分。     

常染色体非特异性精神发育迟滞相关基因研究进展

常染色体上一些基因与神经系统的发育和功能密切相关, 突变后可导致非特异性精神发育迟滞。文章从基因定位、表达、生物学功能与突变后致病机理等方面, 对常染色体非特异性精神发育迟滞相关基因的研究现状进行了综述, 并展望了今后这一领域的研究前景。     

人类Y染色体常染色质部分DNA YAC重叠克隆构建

人类基因组研究的目标在于人类基因组全部DNA的核苷酸顺序的测定,及在此基础上的对所有基因的编码及其生化功能的研究。全基因组DNA的完全的物理图谱构成,包括全基因组DNA的大片段克隆,及覆盖完整基因组的克隆重叠排序是达成这一目标的首要步骤。     

人类人工染色体的构建策略

目前各种应用于基因治疗领域的载体均存在一定的局限性。越来越多的研究认为,最理想的基因治疗载体应该在染色体的结构基础上构建,使目的基因整合舌能够作为独立的功能单位表达,或成为游离基因而稳定存在。人类人工染色体(human artificial chromosome,HAC)的出现,使这种设想成为可能。近年来,研究们基于两种基本策略相继构建多种HAC,并以之作为载体进行了一系列外源性基因表达研究,尽管还有许多问题亟待解决,但并不妨碍人们对之成为理想的基因治疗载体寄予厚望。     

A gradient of silent substitution rate in the human pseudoautosomal region

It has been demonstrated that recombination in the human p-arm pseudoautosomal region (p-PAR) is at least twenty times more frequent than the genomic average of approximately 1 cM/Mb, which may affect substitution patterns and rates in this region. Here I report the analysis of substitution patterns and rates in 10 human, chimpanzee, gorilla, and orangutan genes across the p-PAR. Between species silent divergence in the p-PAR forms a gradient, increasing toward the telomere. The correlation of silent divergence with distance from the p-PAR boundary is highly significant (rho = 0.911, P < 0.001). After exclusion of the CpG dinucleotides this correlation is still significant (rho = 0.89, P < 0.01), thus the substitution rate gradient cannot be explained solely by the differences in the extent of methylation across the p-PAR. Frequent recombination in the PAR may result in a relatively strong effect of biased gene conversion (BGC), which, because of the increased probability of fixation of the G or C nucleotides at (A or T)/(G or C) segregating sites, may affect substitution rates. BGC, however, does not seem to be the factor creating the substitution rate gradient in the p-PAR, because the only gradient is still detactable if only A<-->T and G<-->C substitutions are taken into account (rho = 0.82, P < 0.01). I hypothesize that the substitution rate gradient in the p-PAR is due to the mutagenic effect of recombination, which is very frequent in the distal human p-PAR and might be lower near the p-PAR boundary.     

Molecular evolution of recombination hotspots and highly recombining pseudoautosomal regions in hominoids

We examined the effects of recombination on the molecular evolution of noncoding regions in pseudoautosomal regions (PARs) and recombination hotspots in hominoids. The PAR-linked regions analyzed had on average longer branch lengths than those of the recombination hotspots. Moreover, contrary to previous observations, we found no correlation between recombination rate and silent site divergence in our data set and little change in the GC content during recent hominoid evolution. This suggests that the current rate of recombination is not a good indicator of the past rates of recombination for these highly recombining regions. Furthermore, human recombination hotspots show increased AT to GC substitutions in the human lineage, while no such pattern is detected for PAR-linked regions. Together, these observations suggest that recombination hotspots in hominoids are transient in the evolutionary time-scale. Interestingly, the 16p13.3 recombination hotspot locus violates a local molecular clock, though the locus appears to be noncoding and should evolve neutrally. We hypothesize that sudden changes in recombination rate have caused the changes in substitution rate at this locus.     

The pseudoautosomal regions of the human sex chromosomes

In human females, both X chromosomes are equivalent in size and genetic content, and pairing and recombination can theoretically occur anywhere along their entire length. In human males, however, only small regions of sequence identity exist between the sex chromosomes. Recombination and genetic exchange is restricted to these regions of identity, which cover 2.6 and 0.4 Mbp, respectively, and are located at the tips of the short and the long arm of the X and Y chromosome. The unique biology of these regions has attracted considerable interest, and complete long-range restriction maps as well as comprehensive physical maps of overlapping YAC clones are already available. A dense genetic linkage map has disclosed a high rate of recombination at the short arm telomere. A consequence of the obligatory recombination within the pseudoautosomal region is that genes show only partial sex linkage. Pseudoautosomal genes are also predicted to escape X-inactivation, thus guaranteeing an equal dosage of expressed sequences between the X and Y chromosomes. Gene pairs that are active on the X and Y chromosomes are suggested as candidates for the phenotypes seen in numerical X chromosome disorders, such as Klinefelter's (47,XXY) and Turner's syndrome (45,X). Several new genes have been assigned to the Xp/Yp pseudoautosomal region. Potential associations with clinical disorders such as short stature, one of the Turner features, and psychiatric diseases are discussed. Genes in the Xq/Yq pseudoautosomal region have not been identified to date.     

Insights into chromosomal evolution and sex determination of Pseudobagrus ussuriensis (Bagridae,Siluriformes) based on a chromosome-level genome

Pseudobagrus ussuriensis is an aquaculture catfish with significant sexual dimorphism. In this study, a chromosome-level genome with a size of 741.97 Mb was assembled for female P. ussuriensis. A total of 26 chromosome-level contigs covering 97.34% of the whole-genome assembly were obtained with an N50 of 28.53 Mb and an L50 of 11. A total of 24,075 protein-coding genes were identified, with 91.54% (22,039) genes being functionally annotated. Based on the genome assembly, four chromosome evolution clusters of catfishes were identified and the formation process of P. ussuriensis chromosomes was predicted. A total of 55 sex-related quantitative trait loci (QTLs) with a phenotypic variance explained value of 100% were located on chromosome 8 (chr08). The QTLs and other previously identified sex-specific markers were located in a sex-determining region of 16.83 Mb (from 6.90 to 23.73 Mb) on chr08, which was predicted as the X chromosome. The sex-determining region comprised 554 genes, with 135 of which being differently expressed between males and females/pseudofemales, and 16 candidate sex-determining genes were screened out. The results of this study provided a useful chromosome-level genome for genetic, genomic and evolutionary studies of P. ussuriensis, and also be useful for further studies on sex-determination mechanism analysis and sex-control breeding of this fish.     

Evolutionary dynamics of the human pseudoautosomal regions

Recombination between the X and Y human sex chromosomes is limited to the two pseudoautosomal regions (PARs) that present quite distinct evolutionary origins. Despite the crucial importance for male meiosis, genetic diversity patterns and evolutionary dynamics of these regions are poorly understood. In the present study, we analyzed and compared the genetic diversity of the PAR regions using publicly available genomic sequences encompassing both PAR1 and PAR2. Comparisons were performed through allele diversities, linkage disequilibrium status and recombination frequencies within and between X and Y chromosomes. In agreement with previous studies, we confirmed the role of PAR1 as a male-specific recombination hotspot, but also observed similar characteristic patterns of diversity in both regions although male recombination occurs at PAR2 to a much lower extent (at least one recombination event at PAR1 and in ≈1% in normal male meioses at PAR2). Furthermore, we demonstrate that both PARs harbor significantly different allele frequencies between X and Y chromosomes, which could support that recombination is not sufficient to homogenize the pseudoautosomal gene pool or is counterbalanced by other evolutionary forces. Nevertheless, the observed patterns of diversity are not entirely explainable by sexually antagonistic selection. A better understanding of such processes requires new data from intergenerational transmission studies of PARs, which would be decisive on the elucidation of PARs evolution and their role in male-driven heterosomal aneuploidies.     

Evolutionary breakpoint regions and chromosomal remodeling in Harttia (Siluriformes: Loricariidae) species diversification

The Neotropical armored catfish genus Harttia presents a wide variation of chromosomal rearrangements among its representatives. Studies indicate that translocation and Robertsonian rearrangements have triggered the karyotype evolution in the genus, including differentiation of sex chromosome systems. However, few studies used powerful tools, such as comparative whole chromosome painting, to clarify this highly diversified scenario. Here, we isolated probes from the X₁ (a 5S rDNA carrier) and the X₂ (a 45S rDNA carrier) chromosomes of Harttia punctata, which displays an X₁X₁X₂X₂/X₁X₂Y multiple sex chromosome system. Those probes were applied in other Harttia species to evidence homeologous chromosome blocks. The resulting data reinforce that translocation events played a role in the origin of the X₁X₂Y sex chromosome system in H. punctata. The repositioning of homologous chromosomal blocks carrying rDNA sites among ten Harttia species has also been demonstrated. Anchored to phylogenetic data it was possible to evidence some events of the karyotype diversification of the studied species and to prove an independent origin for the two types of multiple sex chromosomes, XX/XY₁Y₂ and X₁X₁X₂X₂/X₁X₂Y, that occur in Harttia species. The results point to evolutionary breakpoint regions in the genomes within or adjacent to rDNA sites that were widely reused in Harttia chromosome remodeling.     

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。     

Sry基因的研究进展

性别决定基因（Sex region of Y chromosome, 人类以SRY,小鼠以Sry表示）的研究进展是近几年来人类在性别决定,性别分化研究中获得的最大的突破性成果,该文从SRY（Sry)发现前关于性别决定因子的研究,SRY（Sry)的确定,小鼠Sry的结构研究,小鼠Sry的表达研究及Sry下游基因的确定等5个方面对小鼠Sry的研究进展进行综述,对进一步深入研究Sry下游基因存在的瓶颈问题人了一定的分析,并提出核移植技术可能对研究Sry的调节及其下游基因所需的特殊实验材料展现了新的希望。     

蛾类昆虫性信息素生物合成的研究进展

综述了各种不同化学结构类型的蛾类雌性信息素生物合成途径。此外还叙述了特定比例的性信息素成分在雌蛾体内产生的机理以及某些蛾类中信息素生物合成酶类与物种进化间的关系。