果蝇唾腺染色体实验的改进

果蝇唾腺巨型染色体是大约1000-4000多条同源染色线精确配对聚集而成的多线染色体,这是染色体多次复制,但细胞只生长、不分裂的结果.染色体长达0.5mm.粗细是一般体细胞染色体的100-200倍左右,其上有深浅间隔、宽窄不等的染色带,果蝇4对唾腺染色体上已确定了6000多条染色带,它们宽窄、疏密、顺序、数目恒定,有种的特异性,同种个体的是相同的,不同的种则不一样,因此果蝇多线染色体可以建立染色带及间带分布图,它们的表现和遗传学图大致平行,多数遗传学家认为这些横纹与基因有对应关系,     

介绍一种摇蚊唾腺染色体永久封片的制作方法

多线染色体是体细胞分裂间期染色质丝多次复制但不分开形成的。虽然摇蚊多线染色体早在1881年就已被发现,但由于人们缺乏对其遗传学的了解,并未用它做深入的遗传学研究。随着真核生物基因表达研究的深入,多线染色体的斑带及疏松结构再次引起遗传学家的兴趣。摇蚊幼虫个体大、廉价易操作,其唾腺多线染色体明显,故成为理想的遗传学实验材料。对摇蚊唾腺染色体染色方法进行了一些探索。     

多线染色体制片法

多线染色体是一种巨大染色体。由于它存在于一些双翅目昆虫幼虫(如摇蚊幼虫、果蝇幼虫)的唾腺细胞中,所以又称为唾腺染色体。实际它不只存在于唾腺细胞,也存在于其     

果蝇幼虫唾腺染色体标本的制备与比较

唾腺染色体是最早发现于双翅目昆虫唾腺细胞的一种巨大染色体,现已广泛应用于细胞遗传、基因定位等研究中。用黑腹果蝇3龄幼虫为材料,压片法制备染色体标本,并对3种品系果蝇幼虫的唾腺染色体的形态结构进行比较。结果表明:果蝇唾腺染色体臂端粒端的横纹特征基本恒定,是辨认各染色体臂的最便捷方法;黑腹果蝇的3种品系果蝇幼虫在唾腺染色体横纹的宽窄、数目、排列顺序及疏密程度上不存在明显的差异,在不同变种之间无法区分。     

巴氏小体案例在遗传学教学中的应用

细胞遗传学在染色体水平上有3个经典问题,即巴氏小体、多线染色体和灯刷染色体的形成机制和遗传学效应。其中巴氏小体因其与哺乳动物在两性间X染色体的剂量补偿效应、人类性别鉴定和某些人类疾病的相关性而引起科研和教学工作者的持续关注。在遗传学教学过程中,作者尝试将国外的案例教学方式引入教学实践,将巴氏小体这一经典遗传学问题作为一条线贯穿于遗传学教学的部分环节,例如伴性遗传、基因表达调控、癌症发生以及遗传学实验,最后通过课堂讨论会的形式全面总结相关的遗传学知识。结果发现,这种改进的教学方法不仅可以优化遗传学教学内容,拓宽并巩固学生的遗传学基础知识,形成了对一个经典遗传学问题的系统观、发展观;还能引导和激发学生对生命科学的兴趣,收到了良好的教学效果。     

实验用果蝇饲养及保种注意事项

果蝇（Drosophila melanogaste,2n=8）为完全变态的双翅目昆虫,具有生活史短、突变型多、染色体数目少、繁殖率高等突出特点,是遗传学教学中不可缺少的实验材料,也是遗传学研究中经典的模式生物材料。因此,饲养好果蝇对遗传学教学和科学研究有着重要的意义。现将本实验室饲养果蝇和保种方法总结如下。     

灯刷染色体的研究进展及其在遗传学教学中的思考

灯刷染色体是存在于除哺乳动物以外几乎所有动物雌配子减数分裂第一次分裂双线期的一种暂时性巨大转录体,因状如灯刷而得名,但在细胞遗传学三大经典染色体研究中关注度最低。它是研究减数分裂时期染色体的结构、组织形式、转录和转录过程的好材料。本文一方面对以上研究及形成机制作一简要综述,另一方面探讨灯刷染色体可能的作用,也即从已有文献表明卵细胞核的灯刷染色体或多倍化为相关生物胚胎发育提供足够的转录产物。最后探讨将其作为一个案例用于遗传学教学的可能性,以激发学生学习遗传学的兴趣。     

用Feuglen染色法制做果蝇唾腺染色体

制作果蝇唾腺染色体通常以改良苯酚品红或醋酸洋红为染色剂 ,这些常规方法存在 1个共同的弊病 ;染色体被着色的同时 ,细胞质也着色较深 ,染色体与其背景形成的反差很小 ,不利于显微摄影。为此笔者改变传统方法用 Feuglen染色法对果蝇唾腺染色体进行染色制片 ,收到了良好的效果。1　方法和步骤1)将盛有 1mol盐酸的小烧杯置于 6 0℃的恒温水浴中 ,待用 ;2 )取较肥大的果蝇三龄幼虫 ,置于滴有 0 .85 %生理盐水中 ,在解剖镜下剖出唾腺 ;3)弃去杂物 ,剔除唾腺上的脂肪 ;　　 4 )将唾腺小心移至 1mol盐酸的恒温小烧杯中 ,2 0～ 30 s;5 )取出唾腺 …     

“银额果蝇及其B染色体研究”获云南省2000年科学技术二等奖

中国科学院昆明动物研究所凌发瑶等 ,在国家自然科学基金、中国科学院院长基金、日本文部省国际研究基金的支持下 ,从群体细胞遗传学和分子遗传学着手 ,对银额果蝇及其Ｂ染色体的起源、进化以及生物学效应等进行了系统深入的研究。发现我国银额果蝇自然群体内存在极其丰富的Ｂ染色体遗传资源 ,并认为这是一种十分难得的可供持续研究Ｂ染色体的最佳动物模型 ;同时还发现了银额果蝇自然群体进化过程中的中间过渡性新核型 ,这一发现对研究果蝇的系统进化以及染色体的进化方式有着重要意义。通过本项研究 ,查明了银额果蝇自然群体内存在Ｂ染色体…     

实验果蝇的一些饲养技巧和注意事项

果蝇（Drosophila melanogaster）属双翅目小型昆虫,是经典的遗传学实验材料。摩尔根利用果蝇实验发现了连锁互换规律及白眼基因的性连锁遗传,提出基因在染色体上直线排列的论断,其学生穆勒则开创了X射线诱变的先河。目前果蝇还作为人类基因组计划和行为遗传学以及神经生物学的模式生物,可以说果蝇已成为遗传学各分支学科的最常用实验动物之一,实验室培养果蝇是一项基础技术。现介绍笔者在果蝇饲养方面一些技巧和注意事项。     

Whole arm inversions of chromosome 4 in Drosophila species

Inversions of genetic segments during the evolution of Drosophila are well documented in the X chromosome and most autosomes, but little attention has been paid to chromosome 4, the smallest autosome or "dot chromosome" present in many Drosophila species. From our previous mapping we have defined probes that mark proximal, intermediate, and distal locations of chromosome 4 in D. melanogaster. In situ hybridizations on salivary gland polytene chromosomes with these probes show that the whole right arm, including genes within cytological region 101EF-102F, is inverted relative to D. simulans. We also used these probes to determine the orientation of the arm of the dot chromosome in nine species of Drosophila, including eight from the melanogaster subfamily. To account for the observed whole arm inversions of chromosome 4 in five of the nine species examined, we propose that three inversion events have occurred during the evolution of these species. These whole arm inversions may explain some of the unusual features of this chromosome.     

Lethality Patterns and Morphology of Selected Lethal and Semi-Lethal Mutations in the Zeste-White Region of DROSOPHILA MELANOGASTER

Aspects of the developmental genetics of lethal and semi-lethal mutants representing 13 complementation groups (cistrons) in the 3A-3C region of the X chromosome of Drosophila melanogaster are given. Each of these cistrons is associated with a particular chromomere in the salivary gland chromosome. Mutants within each cistron have similar lethality patterns and morphological attributes, and the characteristics of a given cistron are distinct with respect to other cistrons. These results provide additional evidence that only one function is associated with each chromomere.-The results of the lethality pattern analysis are also compared with previous studies of lethal mutants of Drosophila.     

The structural genes for three Drosophila glue proteins reside at a single polytene chromosome puff locus.

The polytene chromosome puff at 68C on the Drosophila melanogaster third chromosome is thought from genetic experiments to contain the structural gene for one of the secreted salivary gland glue polypeptides, sgs-3. Previous work has demonstrated that the DNA included in this puff contains sequences that are transcribed to give three different polyadenylated RNAs that are abundant in third-larval-instar salivary glands. These have been called the group II, group III, and group IV RNAs. In the experiments reported here, we used the nucleotide sequence of the DNA coding for these RNAs to predict some of the physical and chemical properties expected of their protein products, including molecular weight, amino acid composition, and amino acid sequence. Salivary gland polypeptides with molecular weights similar to those expected for the 68C RNA translation products, and with the expected degree of incorporation of different radioactive amino acids, were purified. These proteins were shown by amino acid sequencing to correspond to the protein products of the 68C RNAs. It was further shown that each of these proteins is a part of the secreted salivary gland glue: the group IV RNA codes for the previously described sgs-3, whereas the group II and III RNAs code for the newly identified glue polypeptides sgs-8 and sgs-7.     

Organ formation in Drosophila: specification and morphogenesis of the salivary gland

The Drosophila salivary gland has emerged as an outstanding model system for the process of organ formation. Many of the component steps, from initial regional specification through cell specialization and morphogenesis, are known and many of the genes required for these different processes have been identified. The salivary gland is a relatively simple organ; the entire gland comprises of only two major cell types, which derive from a single contiguous primordium. Salivary cells cease dividing once they are specified, and organ growth is achieved simply by an increase in size of individual cells, thus eliminating concerns about the potential unequal distribution of determinants during mitosis. Drosophila salivary glands form by the same cellular mechanisms as organs in higher organisms, including regulated cell shape changes, cell intercalation and directed cell migration. Thus, learning how these events are coordinated for tissue morphogenesis in an organism for which the genetic and molecular tools are unsurpassed should provide excellent paradigms for dissecting related processes in the more intricate organs of more complicated species.     

The banding pattern of the salivary gland chromosomes of Drosophila hydei

The banding pattern of the salivary gland chromosomes of D. hydei was investigated in the electron microscope. We compared the banding pattern of squashed chromosomes with non-squashed preparations and observed that the fixation and squash procedure we used does not introduce artificial changes in the banding pattern of the chromosome. An electron microscopic map was made of the banding pattern of the distal half of the second salivary gland chromosome. On the basis of the number of bands in this part of the second chromosome we calculated a total of about 3700 bands for the whole set of polytene chromosomes of D. hydei. Our data indicate a similar number of bands in the salivary gland chromosomes of evolutionary remote Drosophila species like D. hydei and D. melanogaster.     

Salivary gland development in Drosophila melanogaster

The Drosophila salivary gland is proving to be an excellent experimental system for understanding how cells commit to specific developmental programs and, once committed, how cells implement such decisions. Through genetic studies, the factors that determine where salivary glands will form, the number of cells committed to a salivary gland fate, and the distinction between the two major cell types (secretory cells and duct cells) have been discovered. Within the next few years, we will learn the molecular details of the interactions among the salivary gland regulators and salivary gland target genes. We will also learn how the early-expressed salivary gland genes coordinate their activities to mediate the morphogenetic movements required to form the salivary gland and the changes in cell physiology required for high secretory activity.     

Sequential gene activation by ecdysteroids in polytene chromosomes ofDrosophila melanogaster

Summary Changes in polytene chromosome 3 L puffing patterns in the fat body ofDrosophila melanogaster larvae and prepupae are compared to those in the salivary gland. While some general features are common to the two tissues, there are differences which reflect their different developmental roles. In vitro experiments with fat body chromosomes show that they have a distinct response to ecdysteroids which is different from that of salivary gland chromosomes, and which does not,in this culture system, reproduce the changes observed in normal development. In short term culture experiments, the fat body chromosomes appear more sensitive to ecdysteroids than the salivary gland chromosomes and, although 20-OH ecdysone is more active than ecdysone in these assays, the possibility is not excluded that ecdysone has a role in normal development as it appears to alter gene activity at physiological levels in these cells.     

A photographic map of Drosophila madeirensis polytene chromosomes.

A photographic map of salivary gland polytene chromosomes of Drosophila madeirensis has been constructed showing homologies and differences with respect to the standard gene arrangement of D. subobscura. Only two paracentric inversions in the X chromosome and some slight minor dissimilarities of one or two bands in the autosomes differentiate the chromosomes of these species.