悦目金蛛(Argiope amoena)染色体的观察

对悦目金株（Ａｒｇｉｏｐｅ ａｍｏｅｎａ）染色体的数目、形态特征和性染色体组成,进行了核型分析,本实验观察胚胎细胞有丝分裂的Ｃ－中期相,悦目金蛛体细胞染色体数目是：雌性２ｎ＝２６,雄性２ｎ＝２４,性别决定机制属于ＸＸＯ型。     

Polysaccharides as Constituents in Chromosome Organization: A Study on Meiotic Chromosomes of Grasshopper and Polytene Chromosomes of Dipterous Flies

Study on meiotic chromosomes of grasshopper, Gesonula punctifrons and interphase polytene chromosomes from Dipteran larvae as of Chironomus striatipennis and Drosophila melanogaster following staining by periodic acid-Schiff technique revealed that chromosomes contained polysaccharides as an integral part of their organization. PAS +ve nature of the chromosomes both at highly condensed state as available during meiotic cell division and at extended state as in polytene chromosomes supports the idea that chromosomes contain polysaccharides as one of the constituent biological macromolecules. PAS +ve chromosomes appeared to be fluorescent under fluorescence microscope and fluorescence was found to be more or less uniform along the whole length of the meiotic chromosomes, while in case of polytene chromosomes intense fluorescence could be noticed along the band regions of the chromosomes.     

A Polymer Model for the Structural Organization of Chromatin Loops and Minibands in Interphase Chromosomes

A quantitative model of interphase chromosome higher-order structure is presented based on the isochore model of the genome and results obtained in the field of copolymer research. G1 chromosomes are approximated in the model as multiblock copolymers of the 30-nm chromatin fiber, which alternately contain two types of 0.5- to 1-Mbp blocks (R and G minibands) differing in GC content and DNA-bound proteins. A G1 chromosome forms a single-chain string of loop clusters (micelles), with each loop ~1–2 Mbp in size. The number of ~20 loops per micelle was estimated from the dependence of geometrical versus genomic distances between two points on a G1 chromosome. The greater degree of chromatin extension in R versus G minibands and a difference in the replication time for these minibands (early S phase for R versus late S phase for G) are explained in this model as a result of the location of R minibands at micelle cores and G minibands at loop apices. The estimated number of micelles per nucleus is close to the observed number of replication clusters at the onset of S phase. A relationship between chromosomal and nuclear sizes for several types of higher eukaryotic cells (insects, plants, and mammals) is well described through the micelle structure of interphase chromosomes. For yeast cells, this relationship is described by a linear coil configuration of chromosomes.     

Nonsomatotopic Organization of the Higher Motor Centers in Octopus

Hyperredundant limbs with a virtually unlimited number of degrees of freedom (DOFs) pose a challenge for both biological and computational systems of motor control. In the flexible arms of the octopus, simplification strategies have evolved to reduce the number of controlled DOFs [1], [2] and [3]. Motor control in the octopus nervous system is hierarchically organized [4] and [5]. A relatively small central brain integrates a huge amount of visual and tactile information from the large optic lobes and the peripheral nervous system of the arms [6], [7], [8] and [9] and issues commands to lower motor centers controlling the elaborated neuromuscular system of the arms. This unique organization raises new questions on the organization of the octopus brain and whether and how it represents the rich movement repertoire. We developed a method of brain microstimulation in freely behaving animals and stimulated the higher motor centers—the basal lobes—thus inducing discrete and complex sets of movements. As stimulation strength increased, complex movements were recruited from basic components shared by different types of movement. We found no stimulation site where movements of a single arm or body part could be elicited. Discrete and complex components have no central topographical organization but are distributed over wide regions.     

Chromosomes of the Lemuridae

Chromosome studies have been made from skin cultures of 23 individual lemurs representing five different species and including Cheirogaleus medius of the Cheirogaleinae. The results are presented in tabular form and are compared with data from other studies. A detailed study of the chromosomes and replication patterns of L. variegatus ruber and L. v. s. did not reveal any distinguishing features between these subspecies.     

Brain Organization in a Reptile Lacking Sex Chromosomes: Effects of Gonadectomy and Exogenous Testosterone

In mammals, males and females differ both genetically and hormonally, making it difficult to assess the relative contributions of genetic constitution and fetal environment in the process of sexual differentiation. Many reptiles lack sex chromosomes, relying instead on the temperature of incubation to determine sex. In the leopard gecko (Eublepharis macularius), an incubation temperature of 26°C produces all females, whereas 32.5°C results in mostly males. Incubation temperature is the primary determinant of differences both within and between the sexes in growth, physiology, and sociosexual behavior, as well as the volume and metabolic capacity of specific brain nuclei. To determine if incubation temperature organizes the brain directly rather than via gonadal sex hormones, the gonads of male and female leopard geckos from the two incubation temperatures were removed and, in some instances, animals were given exogenous testosterone. In vertebrates with sex chromosomes, the size of sexually dimorphic nuclei are sensitive to hormone levels in adulthood, but in all species studied to date, these changes are restricted to the male. Therefore, after behavior tests, morphometrics of certain limbic and nonlimbic brain areas were determined. Because nervous system tissue depends on oxidative metabolism for energy production and the level of cytochrome oxidase activity is coupled to the functional level of neuronal activity, cytochrome oxidase histochemistry also was performed on the same brains. Hormonal manipulation had little effect on the volume of the preoptic area or ventromedial hypothalamus in geckos from the all-female incubation temperature, but significantly influenced the volumes of these brain areas in males and females from the male-biased incubation temperature. A similar relationship was found for cytochrome oxidase activity of the anterior hypothalamus, amygdala, dorsal ventricular ridge, and septum. The only sex difference observed was found in the ventromedial hypothalamus; males showed no significant changes in cytochrome oxidase activity with hormonal manipulation, but females from both incubation temperatures were affected similarly. The results indicate that incubation temperature organizes the brain directly rather than via hormones arising from its sex-determining function. This is the first demonstration in a vertebrate that factors other than steroid hormones can modify the organization and functional activity of sexually differentiated brain areas.