共查询到20条相似文献，搜索用时 171 毫秒
1.
真核细胞的分裂方式主要有两种:有丝分裂和减数分裂.在有丝分裂的过程中,复制后的染色体经过着丝粒分裂,相同的染色体平均分配到两个子细胞中,形成含有与母细胞一样染色体组成的子细胞.在减数分裂过程中,复制后的同源染色体联会后相互分离,结果形成的生殖细胞内的染色体数目为体细胞的一半.无论有丝分裂还是减数分裂,DNA复制差错会导... 相似文献
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采用常规制片技术,对苍山、鸡足山华严寺和昆明长虫山3个四倍体多星韭种群进行了减数分裂观察和核型分析.结果表明：核型分析反映出云南西北部地区的苍山、鸡足山四倍体多星韭的核型对称性比中部地区昆明长虫山种群高;减数分裂观察表明四倍体多星韭的28条染色体在减数分裂前期I时,两两联会成为14个二价体,后期I配对的染色体分离比较同步,没有观察到提前或延后分离以及染色体桥或染色体片段;对四倍体减数分裂过程的观察支持核型分析将28条染色体成2地配成14组,而不是成4地配成7组的结果,为四倍体多星韭的二倍体化提供了直接的细胞学证据. 相似文献
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细胞分裂方式图像检索天津杨柳青一中（３００３８０）方恩亮学生在学习减数分裂与有丝分裂时，总感到不容易区分两种分裂方式的图像。要克服这个难点，我们采取的办法是：根据减数分裂和有丝分裂过程中染色体行为和数目的变化编制出细胞分裂方式图像检索简表，并教会学生... 相似文献
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一、教材分析“减数分裂与有性生殖细胞的成熟”一节,是在学生已学过有丝分裂和有性生殖概念后来学习的,是为以后学习生物个体发育和遗传规律作基础的,是全书的一个重点,也是一个难点。课本中,结合动物的精子和卵细胞的形成过程来讲减数分裂,其中减数分裂的过程是本节的重点,染色体和ＤＮＡ的动态过程是本节的难点。二、教学过程１．复习利用录像放映有丝分裂的过程,让学生回忆有丝分裂各时期的特点和有丝分裂过程中染色体的变化过程。２．新课上面我们复习了有丝分裂的过程,今天我们来学习一种特殊的有丝分裂──减数分裂投影１：… 相似文献
5.
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、教材分析 相似文献
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细胞分裂是生活细胞的重要生理功能之一。细胞分裂的方式有三种：无丝分裂、有丝分裂、减数分裂。对于绝大多数动植物来讲,主要是有丝分裂和减数分裂两种。生物之所以能够在荣代和子代之间保持遗传性状的稳定性．主要是因为在细胞分裂过程中,保持了遗传物质的相对稳定性。而生物的主要遗传物质是DNA染色体又是遗传物质DNA的主要载体,所以在细胞分裂过程中讨论比较多的是染色体和DNA的变化。以下就两种主要分裂方式谈谈DNA和染色体的变化规律。1有丝分裂生物细胞有丝分裂的重要特征,就是亲代细胞的染色体经过复制以后,平均分配到两… 相似文献
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<正>1问题二倍体动物细胞减数分裂和有丝分裂图像是教学中的难点。"三看法"对于帮助学生理解减数分裂和有丝分裂图像的区别,有一定效果。所谓的"三看",是指"一看染色体数目;二看有无同源染色体;三看同源染色体的行为"。部分学生熟悉"三看"后,对此类问题依然容易出差错,如将减数分裂和有丝分裂图像张冠李戴,甚至认为有丝分裂的细胞不存在同源染色体。 相似文献
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细胞分裂是生活细胞的重要生理功能之一.对于绝大多数动植物来讲,细胞分裂主要是有丝分裂和减数分裂两种.学生在学习的过程中经常遇到减数分裂与有丝分裂知识的比较,而这两个过程中共性通用的问题常会成为学生易混淆出错的地方.
1 曲线(图1)
1.1 错误理解
如图1该曲线横坐标是分裂时期,纵坐标是每条染色体上的DNA含量,有很多学生认为该曲线只能代表有丝分裂. 相似文献
11.
玉米单倍体的细胞学研究 总被引：2，自引：0，他引：2
用细胞学方法对10株玉米单倍体的体细胞和性细胞进行染色体行为观察和计数，并对体细胞和性细胞进行了比较．结果表明：玉米单倍体的体细胞和性细胞中均有一定比例的二倍体细胞，体细胞中出现二倍体细胞的百分率平均为0．46％；在花粉母细胞中二倍体细胞的百分率比在体细胞中大大提高了，增加幅度最大的达到了12．86％．体细胞中存在二倍体细胞是性细胞中出现二倍体细胞的前提． 相似文献
12.
Keith S. Taber 《International Journal of Science Education》2013,35(10):1333-1358
This paper reports evidence that learners commonly develop a notion of chemical stability that, whilst drawing upon ideas taught in the curriculum, is nevertheless inconsistent with basic scientific principles. A series of related small‐scale studies show that many college‐level students consider a chemical species with an octet structure, or a full outer shell, will necessarily be more stable than a related species without such an electronic configuration. Whilst this finding is in itself consistent with previous research, the present paper shows how students commonly apply this criterion without consideration of chemical context, or other significant factors such as net charge. Species that would seem highly unstable and non‐viable from chemical considerations, such as Na7?, C4+ and even Cl11?, are commonly judged as being stable. This research shows that many college‐level students are privileging a simple heuristic (species with full outer shells will be stable) when asked about the stability of chemical species at the submicroscopic level, to the exclusion of more pertinent considerations. Some students will even judge an atom in an excited state as more stable than when in the ground state, when an electron is promoted from an inner shell to ‘fill’ the outer shell. It is suggested that the apparently widespread adoption of a perspective that is so at odds with the science in the curriculum is highly significant for the teaching of chemistry, and indicates the need for more detailed studies of how such thinking develops and can be challenged. 相似文献
13.
Seventy-one college general biology students were taught a unit in Mendelian genetics by the traditional lecture method. Emphasis was placed on meiotic formation of gametes, the Law of Segregation, and the Law of Independent Assortment. The Punnett-square model was used for all practice problems. Eight weeks later, a content-validated retention test was given to evaluate the students' retention of problem-solving skills. The test required students to use proportional reasoning (identifying ratios from the Punnett squares), combinatorial reasoning (identifying combinations of gametes from parental genotypes), and probabilistic reasoning (estimating gamete or offspring probabilities). Each of the 71 students was also given three Piagetian interview tasks to evaluate intellectual development in the areas of reasoning under question. The balance-beam task, the electronic switch-box task, and colored squares and diamonds were used to test for proportional reasoning, combinatorial reasoning, and probabilistic reasoning, respectively. Pearson correlations and factor analysis failed to show direct relationships among Piagetian tasks for the three kinds of reasoning and their corresponding occurrence in genetics problems. Some correlations were higher between different reasoning types than between similar types. Analysis of variance showed significant differences for all three reasoning types among concrete-operational, transitional, and formal-operational students with the retention test. Post-hoc analysis of ANOVAs indicated that formal-operational students had significantly more success in the three reasoning areas than transitional students, and transitional students had significantly more success than concrete-operational students. 相似文献
14.
Two common fish species, mosquitofish (Gambusia affinis) and topmouth gudgeon (Pseudorasobora para) were exposed to different concentrations of fenitrothion in static system for 96 h. Hepatic glutathione S-transferase activity
was evaluated after 48 and 96 h pesticide exposure, and was also examined in fish pretreated with pepironyl butoxide and triphenyl
phosphate and then exposed to fenitrothion. Results indicated presence of intense glutathione S-transferase activity in both
species, mosquitofish exhibiting the higher activity. In both species the activity decreased as the concentration of fenitrothion
increased, topmouth gudgeon being more susceptible than mosquitofish. In mosquitofish pretreated with pepironyl butoxide,
glutathione S-transferase activity was increased (11.8%) compared with the control but in topmouth gudgeon it was decreased
(21.6%) at the end of 96 h. Glutathione S-transferase activity was significantly reduced in both species pretreated with triphenyl
phosphate at the end of 96 h exposure, topmouth gudgeon being highly susceptible.
Ph. D. student, from Southern Ethiopia Health Bureau, Center for Health Research, P. O. Box 317, Awassa, F. R. Ethiopia. 相似文献
15.
对长江流域安徽省境内黄鳝体内寄生虫的感染情况进行初步调查,共检出6种寄生蠕虫,其中新棘衣棘头虫感染率最高（41.8％）,其次是鳗鲡独孤吸虫（3.5％）、大型多钩槽绦虫（3.5％）、胃瘤线虫（3.3％）、锯缘叶形吸虫（1.1％）、幼旋尾线虫（0.8％）.新棘衣棘头虫的感染率与黄鳝体长相关,并随季节变化而变化.黄鳝体长小于32.5 cm时,新棘衣棘头虫感染率最低（18.52％）;体长在37.5～42.4 cm时,新棘衣棘头虫感染率最高（46.61％）.新棘衣棘头虫对黄鳝感染率春季最低,秋季感染率最高.黄鳝采集的6个地点寄生虫感染的种类、感染率、感染强度均有所不同.2种寄生虫共感染黄鳝情况较常见,而3种寄生虫共感染比例较低. 相似文献
16.
Stephen R. Hooper Lara-Jeane Costa Matthew McBee Kathleen L. Anderson Donna C. Yerby Sean B. Knuth Amy Childress 《Reading and writing》2011,24(2):221-252
The primary purpose of this study was to examine several key questions related to the neuropsychological contributors to early
written language. First, can we develop an empirical measurement model that encompasses many of the neuropsychological components
that have been deemed as important to the development of written language? Second, once derived, will the neuropsychological
components of this model remain stable over first and second grades or will the model change in its composition? Third, will
the strength of the relationships between neuropsychological components and writing outcomes be constant over time, or will
the strength of the relationships change over time? Finally, will the derived empirical model show significant concurrent
and predictive relationships with written expression? The sample included 205 first grade students recruited from a single
school district who were followed into the second grade via two cohorts: Measures were aligned with major neuropsychological
components as extracted from theoretical models of written expression and available empirical findings examining the neuropsychological
contributors to writing in children. These domains included fine-motor speed, language, short-term memory, long-term memory,
and various attention/executive functions including working memory. Confirmatory factor analyses (CFAs) and longitudinal structural
equation modeling (SEM) methods documented that three core latent traits were present and stable at both grades 1 and 2: Fine-Motor,
Language, and Attention/Executive Functions. The overall model was highly related to written expression and spelling at both
grades 1 and 2, with the first grade latent traits accounting for 52 and 55% of the variance in second grade written expression
and spelling, respectively. At both grades, the Language and Attention/Executive Functions latent traits were more highly
associated with written expression and spelling than the Fine-Motor latent trait. 相似文献
17.
ＤａｍｐｉｎｇＰｒｏｐｅｒｔｙｏｆａＮｅｗＴｙｐｅｏｆＰＭＣｓＣｏｍｐｏｓｉｔｅＨｅＤｅｐｉｎｇ（何德坪）（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｅｒｉｎｇ，ＳｏｕｔｈｅａｓｔＵｎｉｖｅｒｓｉｔｙ，Ｎａｎｊｉｎｇ... 相似文献
18.
Josef Kessler Hans J. Markowitsch Wolfgang Guldin Rudolf Riess Monika Pritzel Maria Streicher Marcus Kerriou 《Learning & behavior》1980,8(3):457-464
The performance of cats, guinea pigs, and mice in a delayed alternation paradigm was compared both during initial learning and following a 10-day retention interval. The testing situation (a modified T-maze), the length of the delay period (10 sec), and the amount of training per session and per week were kept identical for all three species. The results indicated that (1) animals of all three species acquired the task within similar time spans, (2) a considerable variance was apparent in the performance of individual animals independent of their species, and (3) guinea pigs, as a group, appeared to need a somewhat longer time to acquire delayed alternation than did mice and cats. Relearning of the task following the 10-day interval seemed to follow similar laws in all three species. 相似文献
19.
Low phosphorus (P) availability is one of the most important factors limiting plant growth in red soils across southeastern China. Many non-symbiotic microorganisms in rhizosphere can enhance P solubility, but little is known about the magnitude of their phosphorus-solubilizing ability (PSA) and the difference in phosphorus-solubilizing microorganisms (PSM) among plant species. The number of phosphorus-solubilizing microorganisms and their PSA in rhizosphere soils of 19 weed species in a citrus orchard on red soil at Changshan, Zhejiang, China, were investigated. Inorganic P (powdered phosphate rock, PR) and organic P (lecithin, OP) were respectively used as the sole P-source to examine the PSA of isolated microbes. The PS actinomycetes community varied greatly among the different weed rhizospheres while the PS fungus community showed to be most stable to the weed rhizosphere. The highest number of PR-PS and OP-PS bacteria was found in rhizosphere soil of Mollugo pentaphyll, and the highest number of PR-PS and OP-PS actinomycetes was found in rhizosphere soil of Polygonum lapathifolium. The highest number of PR-PS fungi was found in Erigeron annuus and Mollugo pentaphyll rhizosphere soil, and the highest number of OP-PS fungi was found in rhizosphere soil of Mazus stachydifolius. Mazus stachydifolius showed the strongest PR-PS ability (6340.75μg) while Eragrostis pilosa showed the strongest OP-PS ability (1301.84μg). The PR-PS ability and OP-PS ability of Mollugo pentaphyll was 4432.87μg and 1122.05μg respectively. A significant correlation between the number of PR-PSM and OP-PSM was found. Significant correlation was only found between the PR-PS fungi number and its PSA(r=0.75, P<0.05) and between the number of OP-PS fungi and its PSA(r=0.87, P<0.01}). It indicated that plant species had significant influence on components of the non-symbiotic PSM community and their activity in its rhizosphere soil. Fungi play a leading role in phosphorus solubilization in weed rhizopshere. It suggested that weed conservation could benefit soil microbe development in agroecosystems, especially in the initial stage of agroecosystem development because there is less organic carbon in bare soil. The results suggested that weed conservation could increase PSA of PSM. 相似文献
20.
We used a psychophysical method to examine the ability of three corvid species to discern fine-grained spatial information.
Nutcrackers, pinyon jays, and scrub-jays were required to discriminate the distance between two landmarks on a computer screen
in an operant chamber. All three species were able to discriminate between arrays that differed by 20 mm; the discrimination
gradients for scrub-jays and pinyon jays were sharper than those for nutcrackers, however. The results suggest that differences
in spatial memory among these species are not related to differences in fine-grained perception. 相似文献