高中生物课堂教学艺术感悟——我的一堂课《减数分裂》

在高中生物课堂教学中,教师要与学生保持良好的师生关系,合理利用教学资源,并根据教学规律,运用各种教学方法完成制定的教学任务。课堂教学艺术形式多样,本文以《减数分裂》为例,从新课导入的艺术、课堂讲授的艺术、课堂教学组织的艺术和课堂板书的艺术这四个方面,阐述了如何上好这节课,以供同仁参考。

《减数分裂和有性生殖细胞的形成》教学尝试及反思

曾经听过许多同行上《减数分裂和有性生殖细胞的形成》的公开课，有的教师讲得很精彩，分析也很有水准，很到位，调动学生积极参与方面也做得很好，课堂气氛较活跃，使我受益匪浅．但有的教师对这节课的讲解往往不尽如人意，或顾此失彼，或讲解知识有失偏颇．本学期笔者曾经上过该节的复习研究课，下面结合笔者对这节课的教学设计，谈谈做法和反思．

《减数分裂与有性生殖细胞成熟》教学设计

一、教学目的 1.使学生掌握减数分裂的概念、过程和特点,明确减数分裂是生殖细胞形成过程中的一种特殊的有丝分裂方式。 2.了解减数分裂过程中染色体的变化规律,为以后学习遗传变异奠定细胞学基础。 二。

Male Reproductive System and Spermatogenesis in Homoptera(Insecta:Hemiptera)

Morphology of the male reproductive system, chromosome behaviors during meiosis and spem tail structures in Homoptera and Heteroptera are compared in this paper. The sheathed testis is found in Fulgoroidea and Heteroptera, and unsheathed testis occurs in Cicadoidea, Cicadelloidea, Cercopoidea, Membracoidea, Psyloidea, Aphidoidea, Aleyrodoidea and Coccoidea. The testis also can be divide into three types by the shape of testicular follicles. The sphere-shaped type is found in Cicadoidea, Cicadelloidea, Cercopoidea, Membracoidea, Aphidoidea and Aleyrodoidea, the tube-shaped type observed in Fulgoroidea, Psyloidea and Coccoidea, and the lamella-shaped type represented by Heteroptera. It is suggested the unsheathed testis may be the primitive type in Homoptera. Meiosis can be divided into 6 type at least, i.e. 1） Cicadoid type; 2） Fulgoroid type; 3） Psyloid type; 4） Aphidoid type; 5） Aleyrodoid type; and 6） Coccoid type. At least four groups exhibit a diffuse stage during meiosis prophase l, they are Psyloidea, Fulgoroidea, Coccoidea and Heteroptera. Sperm tail structures are similar to those reported from other insects with a typical 9＋9＋2 axoneme except that in Aleyrodoidea and Coccoidea whose sperm tail is degenerated.

Comparative Studies on the Changes of Microtubule Distribution and Reorganization During the Meiotic Stages of Development in Normal (IR36) and a Temperature/photoperiod Sensitive Male Sterile Line (Peiai 64S) of Rice ( Oryza sativa )

Changes in the pattern of organization of microtubules in the meiotic stages of development of pollen (i.e. from pre-meiotic interphase to more or less metaphase I) of a normal (IR36) and a temperature/photoperiod sensitive male sterile line (Peiai 64S) of rice were studied using immunofluorescence confocal microscopy. In IR36, from pre-meiotic interphase to metaphase I, the pattern of microtubule distribution in the meiocytes underwent a series of changes. Some new organizational patterns of microtubules (that have not been described before) were observed during microsporogenesis, including the existence of a broad band of perinuclear microtubules at the diakinesis stage of development. The pattern of microtubule distribution in the meiocytes of the male sterile line, Peiai 64S, was quite different front that seen in IR36. In Peiai 64S, the microtubules showed abnormal patterns of distribution from pre-meiotic interphase to metaphase I. For example the broad band of perinuclear microtubules seen at diakinesis in IR36 was much disorganized and loosened in Peiai 64S. The spindles formed were also very abnormal and different from the normal spindle. The appearance of abnormal microtubule distribution in the early stages of microsporogenesis may contribute to the malformation and ultimate abortion of pollen in Peiai 64S.

Meiotic Behavior of 1BL/1RS Translocation Chromosome and Alien Chromosome in Two Tri-genera Hybrids

The behavior of wheat-rye translocation chromosome and alien chromosome including Thinopyrum and Haynaldia chromosome at meiosis was investigated in two hybrids by fluorescence in situ hybridization (FISH). Misdivision of translocation chromosome at anaphase I and rye chromatin micronucleus at tetrad stage were observed, A plant with one normal 1BL/1RS translocation chromosome and one 1BL/1RS translocation chromosome deleted about 1/3 of rye chromosome arm in length was identified. One plant with wheat-Thinopyrum non-Robertson translocation chromosome was also detected in the F-2 population of Yi4212 x Yi4095. That could be the results of unequal misdivision of wheat-rye 1BL/1RS translocation chromosome and Thinopyrum chromosome during meiosis. No interaction between translocation chromosome and alien chromosome at meiosis was supported by the data of the distribution frequencies of translocation chromosome and Thinopyrum or Haynaldia chromosome in the progeny of two hybrids. The results may be useful to cultivate new germplasms with different length of rye 1R short arm and wheat-alien non-Robertson translocation tines under wheat background.

Combination of Homoeologous Pairing Gene phKL and Ph2-deficiency in Common Wheat and Its Meiotic Behaviors in Hybrids with Alien Species

The combined lines having both phKL and Ph2-deficiency were obtained in the genetic background of common wheat (Triticum aestivum L.) landrace. These lines had normal fertility. In the wheat combined lines X Aegilops variabilis Eig. (or rye), a significant increase in the chiasmata of homoeologous pairing was shown by the phKL+Ph2(-) plants with respect to their phKL+Ph2 sibs, which indicates that Ph2-deficiency and phKL showed an additive effect on promoting pairing. The effects were shown in the increment of rod bivalents, ring bivalents and trivalents and reduction of univalents, of which, reduction of univalents was mainly due to the increment of rod bivalents. The combined lines are probably more desirable materials for alien gene transferring than phKL or Ph2(-) lines alone. In comparison with that of ph1b X Ae. variabilis (or rye), phKL+Ph2(-) X Ae. variabilis (or rye) show higher (or similar) numbers of rod bivalents, while the total chromosome pairing level significantly reduced that ascribed to the decrement in ring bivalents and multivalents. These results probably indicate the different genetic mechanisms for Ph1 and Ph2 or phKL on controlling homoeologous pairing.

Pollen Mother Cell Miosis and Male Gametophyte Development of Pumpkin

[Objective] Pollen mother cell miosis and male gametophyte development of pumpkin were observed in this study, to provide some cytological basis for pumpkin anther or microspore culture. [Method] Ehrlich＇s hematoxylin staining-methyl salicylate clearing technique was used for observation and research of the variation of cell structure and chromosomal behavior during pollen mother cell miosis and male gametophyte development of ‘Tianhong＇ pumpkin. [Result] The meiosis in pollen moth- er cells of pumpkin was simultaneous cytokinesis. In the process of nuclear division, nuclear membrane and nucleolus of pumpkin pollen mother cells gradually disappeared in the metaphase I and reappeared in telophase I , phragmoplast formed between the two generated crescent-shaped nuclei without cell wall, the phragmoplast gradually disappeared in the metaphase II and reappeared in telophase II. Phragmoplast spread outward from the center of spindle during the second division was connected with that formed on the central interface of two nuclei during the first division, cell wall of microspores generated from periphery to center. Most of the tetrads contained four sub-cells while a few contained extra small cells. During the period of uniuclete microspore at periphery, the single nucleolus split into 2-3 or more small nucleoli, mature pollen grain was two-celled. Mononucleate pollen cells were mostly appeared in the flower buds with length of 1.0-2.0 cm, which could be used as an important indicator to collect materials for anther or microspore culture. [Conclusion] This study laid the foundation for research of the cytogenetics of pumpkin.

Localization of Phosphorylated Histone H3 at Mitosis and Meiosis in Wheat

One of the prominent cell cycle related modifications of histone proteins, whose function is correlated with chromosome condensation, is the phosphorylation of histone H3. Wheat (Triticum aestivum L.) mitotic and meiotic cells were analyzed with indirect immunoflurorescence labeling with an antibody recognizing histone H3 phosphorylated at Serine 10 to study the localization of phosphorylated histone H3 at mitosis and meiosis. Our results showed that, during mitotic division, the phosphoryiation of H3 started from early prophase and vanished at telophase, remaining mainly in the pericentromeric regions at metaphase and anaphase. During meiotic division, phosphorylation of H3 initiated at the transition from leptotene to zygotene and remained uniform, along the chromosomes from prophase I until telophase whereas it showed slightly stronger in the pericentromeric regions than along the chromosome arms from metaphase II until Lelophase II The different patterns of H3 phophorylation at mitosis and meiosis in wheat suggested that this evolutionarily conserved post-translational chromatin modification might be involved in more roles besides chromosome condensation.

Studies of the Chromosomes in Six Species of the Genus Eurhadina Haupt (Hemiptera:Cicadellidae:Typhlocybinae:Typhlocybini)

Male meiosis karyotypes of 6 chromosome numbers varied from n = 7 bouquet stage is common at prophase. species of Eurhadina Haupt were studied. The to 9. All have XX/XO sex determination. A

Observation of Mitosis and Meiosis in Rice Cells by Simple Squash Method

[Objective] The aim of this study was to establish a feasible squashing technique for chromosome and obtain data of rice chromosome. [Method] With the materials of rice root tips and anther, the specimen was prepared by the modified squash method, and microscopic observation of mitosis and meiosis in rice cells was also carried out. [ Result] Mitosis in rice cells included interphase, prophase, metaphase, anaphase and telophase. Chromosome in metaphase shortened to the minmum, which was a good time for observing and investigating chromosome. However, meiosis in rice cells included meiosis Ⅰ and meiosis Ⅱ. Chromosome replication appeared in meiosis Ⅰ, while cell division only appeared in meiosis Ⅱ. [ Conclusion] The modified squashing technique for rice chromosome can obtain accurate data of rice chromosome, which provides evidence for genetic breeding.

Support vector machine for prediction of meiotic recombination hotspots and coldspots in Saccharomyces cerevisiae

A novel method for predicting hotspots and coldspots using support vector machine （SVM） based on statistical learning theory is developed. This method is applied to published 303 hot and 48 cold open reading frames （ORFs） in Saccharomyces cerevisiae. The sequence features of general dinucleotide abundance and dinucleotide abundance based on codon usage are extracted, and then the data sets are classified with different parameters and kernel functions combined with the method of two-fold cross validation. The result indicates that 87.47% accuracy can be reached when classifying hot and cold ORF sequences with the kernel of radial basis function combined with dinucleotide abundance based on codon usage.

Functional conservation of the meiotic genes SDS and RCK in male meiosis in the monocot rice

The Arabidopsis SDS （SOLO DANCERS） and RCK （ROCK-N-ROLLERS） genes are important for male meiosis, but it is still unknown whether they represent conserved functions in plants. We have performed phylogenetic analyses of SDS and RCK and their respective homologs, and identified their putative orthologs in poplar and rice. Quantitative real-time RT-PCR analysis indicated that rice SDS and RCK are expressed preferentially in young flowers, and transgenic RNAi rice lines with reduced expression of these genes exhibited normal vegetative development, but showed significantly reduced fertility with partially sterile flowers and defective pollens. SDS deficiency also caused a decrease in pollen amounts. Further cytological examination of male meiocytes revealed that the SDS deficiency led to defects in homolog interaction and bivalent formation in meiotic prophase I, and RCK deficiency resulted in defective meiotic crossover formation. These results indicate that rice SDS and RCK genes have similar functions to their Arabidopsis orthologs. Because rice and Arabidopsis, respectively, are members of monocots and eudicots, two largest groups of flowering plants, our results suggest that the functions of SDS and RCK are likely conserved in flowering plants.

The Arabidopsis MutS homolog AtMSH5 is required for normal meiosis

MSH5, a member of the MutS homolog DNA mismatch repair protein family, has been shown to be required for proper homologous chromosome recombination in diverse organisms such as mouse, budding yeast and Caenorhabditis elegans. In this paper, we show that a mutant Arabidopsis plant carrying the putative disrupted AtMSH5 gene exhibits defects during meiotic division, producing a proportion of nonviable pollen grains and abnormal embryo sacs, and thereby leading to a decrease in fertility. AtMSH5 expression is confined to meiotic floral buds, which is consistent with a possible role during meiosis. Cytological analysis of male meiosis revealed the presence of numerous univalents from diplotene to metaphase I, which were associated with a great reduction in chiasma frequencies. The average number of residual chiasmata in the mutant is reduced to 2.54 per meiocyte, which accounts for ~25% of the amount in the wild type. Here, quantitative cytogenetical analysis reveals that the residual chiasmata in Afresh5 mutants are randomly distributed among meiocytes, suggesting that AtMSH5 has an essential role during interferencesensitive chiasma formation. Taken together, the evidence indicates that AtMSH5 promotes homologous recombination through facilitating chiasma formation during prophase Ⅰ in Arabidopsis.

Effects of MEK inhibitor U0126 on meiotic progression in mouse oocytes: microtuble organization, asymmetric division and metaphase Ⅱ arrest

In this study we used U0126, a potent and specific inhibitor of MEK, to study the roles of MEK/ERK/p90rsk signaling pathway in the meiotic cell cycle of mouse oocytes. The phosphorylation of MAP kinase and p90rsk in the oocytes treated with 1.5 μMU0126 was the same as that in oocytes cultured in drug-free medium. With 1.5 μM U0126 treatment, the spindles appeared normal as they formed in oocytes, but failed to maintain its structure.Instead, the spindle lost one pole or elongated extraordinarily. After further culture, some oocytes extruded gigantic polar bodies (＞30 μm) that later divided into two small ones. Some oocytes underwent symmetric division and produced two equal-size daughter cells in which normal spindles formed. In oocytes with different division patterns,MAP kinase was normally phosphorylated. When the concentration of U0126 was increased to 15 mM, the phosphorylation of both MAPK and p90rsk were inhibited, while symmetric division was decreased. When incubating in medium containing 15 μM U0126 for 14 h, oocytes were activated, but part of them failed to emit polar bodies. MII oocytes were also activated by 15 μM U0126, at the same time the dephosphorylation of MAP kinase and p90rsk was observed. Our results indicate that 1) MEK plays important but not indispensable roles in microtubule organization;2) MEK keeps normal meiotic spindle morphology, targets peripheral spindle positioning and regulates asymmetric division by activating some unknown substrates other than MAP kinase/p90rsk; and 3) activation of MEK/ERK/p90rsk cascade maintains MII arrest in mouse oocytes.

Comparative investigation on spindle behavior and MPF activity changes during oocyte maturation between gynogenetic and amphimictic crucian carp

The spindle behavior and MPF activity changes in the progression of oocyte maturation were investigated and compared with cytological observation and kinase assay between gynogenetic silver crucian carp and amphimictic colored crucian carp. MPF activity was measured by using histone H1 as phosphorylation substrate. There were two similar oscillatory MPF kinase activity changes during oocyte maturation in two kinds of fishes with different reproductive modes, but there existed some subtle difference between them. The subtle difference was that the first peak of MPF kinase activity was kept to a longerlasting time in the gynogenetic silver crucian carp than in the amphimictic colored crucian carp. It was suggested that the difference may be related to the spindle behavior changes, such as tripolar spindle formation and spindle rearrangement in the gynogenetic crucian carp.

Low temperature induces oocytes p34^(cdc2) synthesis and accumulation-the acquisition of competence to resume meiosis in toad oocytes

Full grown oocytes derived from Bufo Bufo gargarizans rearing at high temperature environment (24℃),never underwent GVBD after progesterone treatment. No p34cdc2, H1 kinase activity was detected in the oocytes after progesterone stimulation or OA microinjection; Western blotting analysis showed that the level of p3cdc2, and p33 in the oocytes are significantly lower than those in the oocytes derived from the hibernating toads (below 10 ℃). 25S-Met incorporation analysis showed that when the oocytes were incubated at 6℃, synthesis of about thirty defferent polypeptides was promoted or induced, including p34cdc2 and some other p13suc1-binding proteins. All these results indicated that a low temperature environment is essential for the oocytes of Bufo Bufo gargarizans to express and store some cell cycle drivers and its regulators, and to gain the maturation competence. These results will also provide a new clue for explaining the molecular mechanisms why gametogenesis of some organisms depends on a relative low temperature and how to maintain the geographical distribution of some animals.

Identification of differentially expressed genes of primary spermatocyte against round spermatid isolated from human testis using the laser capture microdissection technique

The method of laser capture microdissection (LCM) combined with suppressive subtractive hybridization (SSH) was developed to isolate specific germ cells from human testis sections and to identify the genes expressed during differentiation and development. In the present study, over 10,000 primary spermatocytes and round spermatid cells were successfully isolated by LCM. Using the cDNAs from primary spermatocytes and round spermatids, SSH cDNAs library of primary spermatocyte-specific was constructed. The average insert size of the cDNA isolated from 75 randomly picked white clones was 500 bp, ranging from 250 bp to 1.7 kb. Using the dot-blot method, a total of 421 clones were examined, resulting in the identification of 390 positive clones emitting strong signals. Partial sequence of cDNAs prepared from each clone was determined with an overall success rate of 84.4%. Genes encoding cytochrome c oxidase II and the rescue factor-humanin were most frequently expressed in primary spermatocytes, suggesting their roles involved in meiosis.

Pins homolog LGN regulates meiotic spindle organization in mouse oocytes

Mouse oocytes undergo polarization during meiotic maturation, and this polarization is essential for asymmetric cell divisions that maximize retention of maternal components required for early development. Without conventional centrosomes, the meiotic spindle has less focused poles and is barrel-shaped. The migration of meiotic spindles to the cortex is accompanied by a local reorganization and polarization of the cortex. LGN is a conserved protein involved in cell polarity and regulation of spindle organization. In the present study, we characterized the localization dynamics of LGN during mouse oocyte maturation and analyzed the effects of LGN upregulation and downregulation on meiotic spindle organization. At the germinal vesicle stage, LGN is distributed both cytoplasmically and at the cortex. During maturation, LGN localizes to the meiotic spindle apparatus and cortical LGN becomes less concentrated at the actin cap region. Excessive LGN induces meiotic spindle organization defects by elongating the spindle and enhancing pole focusing, whereas depletion of LGN by RNA interference results in meiotic spindle deformation and chromosome misalignment. Furthermore, the N-terminus of LGN has the ability of full-length LGN to regulate spindle organization, whereas the C-terminus of LGN controls cortical localization and polarization. Our results reveal that LGN is cortically polarized in mouse oocytes and is critical for meiotic spindle organization.

Predicting the Reproduction Strategies of Several Microalgae Through Their Genome Sequences

Documenting the sex and sexual reproduction of the microalgae is very difficult, as most of the results are based on the microscopic observation that can be heavily influenced by genetic, physiological and environmental conditions. Understanding the reproduction strategy of some microalgae is required to breed them in large scale culture industry. Instead of direct observation of sex and sexual reproduction under microscope, the whole set or the majority of core meiosis genes may evidence the sex and sexual reproduction in the unicellular algae, as the meiosis is necessary for maintaining the genomic stability and the advantages of genetic recombination. So far, the available genome sequences and bioinformatic tools （in this study, homolog searching and phylogenetic analysis） allow us to propose that at least 20 core meiosis genes （among them 〉6 must be meiosis specific） are enough for an alga to maintain its sexual reproduction. According to this assumption and the genome sequences, it is possible that sexual reproduction was carried out by Micromonas pusilla and Cyanidiosehyzon merolae, while asexual reproduction was adopted by Bigelowiella natans, Guillardia theta, Nannochloropsis gaditana, N. oeeanica, Chlorella variablis, Phaeodactylum tricornutum and Thalassiosira pseu- donana. This understanding will facilitate the breeding trials of some economic microalgae （e.g., N. gaditana, N. oceanica, C. vari- ablis and P. tricornutum）. However, the reproduction strategies of these microalgae need to be proved by further biological experiments.