Genetic analysis of the wing-form determination of the small brown planthopper,Laodelphax striatellus (Hemiptera: Delphacidae)

The mechanism of the genetic control of wing form determination of the small brown planthopper Laodelphax striatellus was analyzed by selection and crossing experiments. The selection experiment for brachypterous and macropterous forms for 13 generations showed that the wing form is under some genetic control. The crossing experiment showed that the wing form polymorphism was not a simple Mendelian character but was under polygenic control. The data from the crossing experiment were applied to the liability method for the quantitative genetics by Falconer (1981). The analysis suggested that wing form determination was a threshold character under polygenic control, and the estimated minimum number of loci concerned was 2.07. The realized heritability estimated from the data of selection experiment was 0.36 for macroptery. On the other hand, the heritability in broad sense estimated on the basis of the variance of F₁ and F₂ in crossing experiment was 0.81.     

Redesigning the bean seed germination experiment: an activity sheet suggestion

Abstract

Germinating a seed is presumably the first experiment made by a child in his life. So, it has an important place both in child’s scientific experience and understanding. Despite the significance of the experiment, the literature indicates that students possess various misconceptions related to the concepts of seed and seed germination. So, it is thought that this experiment should be focused on in more detail. The purpose of this paper is presenting a proper activity sheet for middle school students to perform this experiment effectively. Science teachers might follow it as an instructional tool in their courses. Thus it is expected to assist students explore the factors which are affective on bean seed germination.     

Age-related changes in crossing over in Drosophila resemble the picture of interchromosomal effect of chromosome rearrangement on crossing over

Crossing over in the left arm of chromosome 2 (2L) was studied in successive broods of Drosophila melanogaster females carrying intact chromosomes (+/+), inversion Muller-5 in the X chromosome (M-5/+), and insertion of the Y-chromosome material into region 34A (Is(2L)/+). The regions net-dp, dp-b, b-pr and pr-cn were examined in 14 two-day-old broods of females +/+ and M-5/+ and in 10 broods of females Is(2L)/+. In all lines, the highest level of crossing over was in the first three broods (eggs laid during the first 6 days of oviposition) and the lowest level in the broods 7-8 (eggs laid at days 14-16). A high rate of crossing over in the first broods of females +/+ and M-5/+ was due to an increment of exchanges in the proximal euchromatin regions (b-pr and pr-cn) and to an increase in the number of tetrads with double exchanges. These changes are similar to a pattern of the interchromosomal effect on crossing over (IEC) in structurally normal chromosomes. In Is(2L)/+ females, a high level of crossing over was due to extensive exchanges in the interstitial regions net-dp and dp and an increase in the number of tetrads with single exchanges. These changes resembled the IEC in rearranged chromosomes (in this case, in chromosomes bearing an insertion). Thus, the age changes of crossing over are similar to the consequences of the presence or absence of IEC. Age changes in crossing over in a chromosome depended both on the local rearrangements in this chromosome (the local effect on crossing over, LEC) and on rearrangements in nonhomologous chromosomes (IEC). In the first broods, both LEC and IEC decreased with an increase in the level of crossing over. In subsequent broods, the reduced level of crossing over was accompanied by an increase in both LEC and IEC. This suggests that the mechanisms responsible for the age changes in crossing over and IEC may have common steps. The contact model of crossing over may explain the similarity between the age changes in crossing-over and IEC. It is suggested that both phenomena result from delayed determination of crossing over in a meiotic cell. This may occur due to the retarded formation of the local contacts in one of the homologous chromosome pairs or because a higher number of local contacts is required to trigger crossing over in a meiotic cell (of early age).     

Mitotic recombination in yeast

Mitotic crossing over in diploid cells, heterozygous for a recessive mutation, results in homozygosis and phenotypic expression of the mutant allele. In addition to crossing over, gene conversion also takes place during mitotic growth. As in meiosis, gene conversion and crossing over are associated.     

杂交试验中的最佳样本含量

杂交试验是一项费时费钱的工作,因此在进行试验之前如能进行严密的设计,给出试验所需的样本大小是十分必要的,统计学中常见的估计样本容理的公式不宜应用于杂交试验,本文分两种情况给出了杂交试验中样本容量的估计公式,据此估计出的样本容量安排杂交试验,可在满足试验者要求的条件下,使试验的总成本最低或使试畜的总头数最少。     

The relationship between homology length and crossing over during the repair of a broken chromosome

Homologous recombination can result in the transfer of genetic information from one DNA molecule to another (gene conversion). These events are often accompanied by a reciprocal exchange between the interacting molecules (termed "crossing over"). This association suggests that the two types of events could be mechanistically related. We have analyzed the repair, by homologous recombination, of a broken chromosome in yeast. We show that gene conversion can be uncoupled from crossing over when the length of homology of the interacting substrates is below a certain threshold. In addition, a minimal length of homology on each broken chromosomal arm is needed for crossing over. We also show that the coupling between gene conversion and crossing over is affected by the mismatch repair system; mutations in the MSH2 or MSH6 genes cause an increase in the crossing over observed for short alleles. Our results provide a mechanism to explain how chromosomal recombinational repair can take place without altering the stability of the genome.     

The genetics of selfing with concurrent backcrossing in breeding hybrid sugar beet (Beta vulgaris altissima L.)

 Sugar beet hybrids are produced by crossing a cytoplasmic male-sterile (CMS) line with a pollinator. New CMS lines are produced by crossing a fertile plant to an existing CMS line. The fertile plant is also selfed. In the following generation, one of the selfed, fertile progeny is paired and isolated with one of the crossed, CMS progeny, to give a second generation of selfing and crossing. Over a series of such crosses and selfs, a new fertile inbred line and its corresponding, near-isogenic CMS partner are produced. Selection among lines takes place at one or more stages of the backcrossing programme. A method is presented here for calculating the genetic variances and covariances within and between lines and generations based on a derivation of additive genetic relationships modified from an approach widely employed in animal breeding. The genetic variances and covariances are used to predict response to selection from varying strategies, from which optimum schemes can be determined. Results suggest that selection should generally take place after three generations of backcrossing when the fertile plant used to initiate the backcrossing process is not inbred, but can take place after generation two when the fertile plant is inbred. Doubled haploid production is unlikely to provide an extra advantage that would be worthwhile in such a system. The method developed here can be used to explore a wide range of more complex breeding systems. Received: 27 July 1998 / Accepted: 19 October 1998     

Confirmation of QTL controlling seed yield in spring canola (Brassica napus L.) hybrids

Allelic effects observed in QTL discovery experiments must be confirmed to be useful in subsequent breeding efforts. Two QTL affecting seed yield of spring hybrid canola (Brassica napus L.) were previously identified in two populations of inbred backcross lines (IBLs) containing germplasm introgressed from a winter cultivar. The effects of favorable alleles at these QTL were retested by crossing two selected IBLs (M5 and M31) to three spring canola lines having different genetic backgrounds. Doubled haploid (DH) lines derived from each F₁ were genotyped with RFLP markers flanking the QTL and grouped into the four possible QTL genotypes. For the first field experiment, DH lines derived by crossing the M5 line to one spring line were crossed to two female testers and evaluated as individual testcross progenies in one environment. QTL genotypes had large variances and were not significantly different. A second field experiment was conducted using the DH lines from the first experiment and two other sets of DH lines derived from the M31 line crossed to two different spring canola lines. Individual lines within each QTL genotype of each set were bulked and crossed to the same testers used in Experiment 1. Bulked hybrid seeds of each QTL genotype were planted in a split-split plot randomized block design and 12 replicates. QTL genotypes had smaller variances in this experiment, and the effects of one QTL were confirmed in some genetic backgrounds. These results suggest that bulking of QTL genotypes and use of an appropriate experimental design with many replicates are needed to detect small differences between QTL genotypes.     

The Evolution of Restricted Recombination and the Accumulation of Repeated DNA Sequences

We suggest hypotheses to account for two major features of chromosomal organization in higher eukaryotes. The first of these is the general restriction of crossing over in the neighborhood of centromeres and telomeres. We propose that this is a consequence of selection for reduced rates of unequal exchange between repeated DNA sequences for which the copy number is subject to stabilizing selection: microtubule binding sites, in the case of centromeres, and the short repeated sequences needed for terminal replication of a linear DNA molecule, in the case of telomeres. An association between proximal crossing over and nondisjunction would also favor the restriction of crossing over near the centromere. The second feature is the association between highly repeated DNA sequences of no obvious functional significance and regions of restricted crossing over. We show that highly repeated sequences are likely to persist longest (over evolutionary time) when crossing over is infrequent. This is because unequal exchange among repeated sequences generates single copy sequences, and a population that becomes fixed for a single copy sequence by drift remains in this state indefinitely (in the absence of gene amplification processes). Increased rates of exchange thus speed up the process of stochastic loss of repeated sequences.     

Hippocampus-dependent retrieval and hippocampus-independent extinction of place avoidance navigation,and stress-induced out-of-context activation of a memory revealed by reversible lesion experiments in rats

The use of reversible lesion techniques in memory research was pioneered in the laboratory of Jan Bures and Olga Buresova. We use the occasion of Jan's 75th birthday to briefly review the experimental utility of this approach. Two experiments from our current research are reported in which reversible lesioning methods are used to ask otherwise experimentally untenable questions about memory retrieval. The first experiment used intra-hippocampal injections of tetrodotoxin to temporarily inactivate the hippocampus during retrieval of a well-learned place avoidance navigation memory. This revealed that the hippocampus is necessary for place avoidance retrieval but that the extinction of place avoidance can occur independently of retrieving the memory and intact hippocampal function. The second experiment used KCl-induced cortical spreading depression in an interhippocampal transfer paradigm to demonstrate that a Y-maze memory that is learned by only one cortical hemisphere can be made to transfer to the other hemisphere by forcing the rat to swim, a unique stressful experience that occurred in a different apparatus, different behavioral context, and involved different behaviors than the Y-maze training. This demonstrates, we believe for the first time behaviorally, that memories can be activated outside of the behavioral context of their acquisition and expression in rats.     

Predation on Atlantic salmon and sea trout during their first days as postsmolts

Radio-tagged smolts of Atlantic salmon Salmo salar and sea trout Salmo trutta were predated heavily by sea birds after crossing the saline limit in the estuary of the River Skjern, Denmark. Most predation took place within the first 9 h after estuarine entry. The field data do not contradict the hypothesis of maladaptive anti-predatory behaviour.     

From the phenomenon of nondisjunction to the problem of chromosome co-orientation (75th anniversary of Bridges' article]

The concepts of the mechanism of chromosome nondisjunction in Drosophila are described in a historical retrospective. Evidences are given for the appropriateness of the term co-orientation in the traditional sense used by geneticists treating nondisjunction. There are 6 variants of co-operation in Drosophila meiosis depending upon the number and particular chromosomes involved in co-orientation. The classical chromosome nondisjunction is a variant of co-orientation in the bivalent composed of two homologous chromosomes. By comparing the different variants of pairing (pairing in bi- and multivalents) resulting in co-orientation, the elementary events preceding co-orientation may be identified. The author reviews his recent data concerning the similarities of the co-orientation of two homologs and the co-orientation of two nonhomologs in Drosophila meiosis. The concept of the role of pairing in the precentromeric heterochromatic region during chromosome co-orientation is considered, and the hypothesis of delayed pairing in this region during meiotic prophase is put forward. Based on the suggested hypothesis clarified are (i) the relationship of pairing, crossing over, and disjunction of homologous chromosomes (ii) the relationship of crossing over and co-orientation of nonhomologous chromosomes, and (iii) the time when the contact resulting in nonhomolog co-orientation takes place.     

Biofeedback and applied psychophysiology at the crossroads

Biofeedback and applied psychophysiology, as tools, as objects of scientific inquiry, and as clinical interventions, have progressed from speculative experiment to data-based research, from trial clinical intervention to efficacy studies and accountability. These are multidisciplinary approaches, crossing the boundary between traditional professions such as medicine, psychology, physical therapy, occupational therapy, and other health care related fields. Along the way we as an Association, our members both scientists and practitioners, have encountered the many hurdles and stumbling blocks that stand in the way of developing new technologies. How we deal with these obstacles shapes us as a group and shapes the perceptions of others who view us. An attempt will be made to place the current development of the field within the context of the rapidly changing health care environment, and to address the challenges, and sometimes conflicting demands, of experimental science and clinical practice.     

Methods for Inducing Selfing, Selfing and Its Role in the Life Cycle of Euplotes woodruffi syngen 3 (Ciliophora)

Methods for inducing selfing, and the relation between selfing and the life cycle of Euplotes woodruffi syngen 3 are reported. Three intercrossing stocks were used in this experiment. Selfing was induced with several treatments as follows: cell-free fluid from the cultures of complementary mating types; intact cells of GI or S phase in the cell cycle; heat-killed cells, and lysed cells of GI-, S-, and D-phase cells which were prepared by freeze-thawing. Stock SJ-27 was used as a parental stock from which Fl clones were originated through selfing. The other two stocks, SJ-8 and SJ-19, were used as testers. The period of immaturity varied from clone to clone. The heterotypic conjugation of clones with cells of stock SJ-8 seems to occur earlier in the life cycle than with cells of stock SJ-19. This result shows that this syngen has an adolescent period in the life cycle. The length of selfing immaturity seems to be different from that of crossing immaturity, and selfing appeared slightly later than crossing with testers. But the clones in which selfing 1st occurred are considered to be in adolescence or maturity, not in senility. Once selfing appeared in any clone, the clone continued to produce selfing pairs till just before clonal death. The viability of selfing and of outcrossing were compared and found not significantly different. Inbreeding depression took place in some of the F2 clones by successive selfing. The viability of F2 clones from young parents was significantly higher than that from old parents (220 to 230 fissions) both in selfing and outcrossing. The total life spans which were studied in three F1 clones were 168 to 264 fissions.     

Non-linearities in cortical simple cells and the possible detection of zero crossings

A theory of early visual information processing proposed by Marr and co-workers suggests that simple cortical cells may be involved in the detection of zero crossing in the retinal output. We have tested this theory by using pairs of adjacent edges (staircases stimuli) and recording from edge-specific simple cells in cat striate cortex. The zero crossing hypothesis gives rise for such stimuli to non-obvious predictions that were generally confirmed by the experiment.     

跑台运动促进幼龄大鼠学习能力

为了探讨跑台运动对幼龄大鼠学习能力的影响,实验采用5周龄Sprague-Dawley大鼠,随机分为安静对照组和跑台运动组,其中跑台运动组大鼠以低强度进行为期一周的跑台运动;然后使用Morris水迷宫,对两组大鼠的定位航行和空间探索能力进行分析。在定位航行实验中,运动组大鼠寻找到平台的潜伏期明显短于对照组（P〈0．05）;并且随着训练次数的增加,运动组大鼠的游泳速度明显高于对照组（P〈0．01）;另外,运动轨迹的弯曲度表明运动组大鼠还表现出了较强的寻找平台的动机以及对平台位置较为准确的空间定位能力。在空间探索实验中,两组大鼠的游泳速度并没有明显差异,从大鼠在各象限内穿越平台相应位置的次数来看,运动组大鼠在D象限穿越的次数高于对照组,但无统计学差异（P〉0．05）。上述结果提示,低强度的跑台运动在短时间内便可以明显提高幼龄大鼠的学习能力。     

Analysis of the genetic effects for several traits in oil palm (Elaeis guineensis Jacq.) populations. I. Population means

An oil palm experiment was set up in the Ivory Coast to compare the effects of crossing and selfing within two origins, Deli and La Mé, on the mean and the variability of Deli x Mé between-origin hybrids. The originality of the experiment lay in the crossing plan, which provided access to genetic parameters related to additivity, dominance and different components of epistasis. This first part covers the analysis of the components of the mean. The parents used were obtained from four palms, two from each origin. Those of La Mé origin were half-sibs. The common parent came from a wild stand in the Ivory Coast. Those of Deli origin were from two different populations bred in Southeast Asia for several generations from a narrow genetic base. These four parents gave rise to nine Deli x La Mé hybrid populations with double-cousintype links. The additive component is more important within the Deli origin than within the La Mé origin. This may be explained by the large genetic divergence between the two Deli parent palms. On the other hand, the additive^* additive epistasis is more substantial within the La Mé origin, probably because of inbreeding. The discussion concentrates on how this information should be used when choosing parents to be crossed and tested and to produce improved populations. The crossing plan proposed can be of general use and is suitable for other species in a reciprocal recurrent selection programme.     

Testing for sex differences in biparental inbreeding and its consequences in a gynodioecious species

In many gynodioecious species cross-pollinated seeds from females outperform those from hermaphrodites. Using the gynodioecious alpine perennial Silene acaulis, I investigated whether this was the result of greater biparental inbreeding among hermaphrodites leading to greater biparental inbreeding depression. I also determined the influence of relatedness on progeny fitness. Experiments were performed using individuals from a site whose population structure and coefficient of inbreeding was known. In the first experiment, crosses were made on plants in the field to determine the effect of seven different crossing distances, plus selfing, on germination and early seedling survival and growth. Although selfed seeds died more often and grew slower than crossed seeds, the effect of crossing distance was negligible for all measured fitness traits, refuting the biparental inbreeding hypothesis as a mechanism to explain why seeds from hermaphrodites die more often than those from females. Nonetheless, cross-pollinated seeds from hermaphrodites did die more, indicating that another mechanism must be responsible. In the second experiment, the effect of different levels of inbreeding on germination and seedling survival was determined by growing seeds from experimental matings varying in relatedness. Inbreeding depression for a multiplicative fitness estimate was significant for all levels of inbreeding, suggesting that inbred individuals are unlikely to become established in the population and providing insight into the results of the first experiment. Alternative hypotheses are discussed to explain why seeds from hermaphrodites die more often, which together with the results of this study, suggest that the restoration of male function in hermaphrodites comes with a correlated cost to seedling survival.     

Systematic mutagenesis of the Saccharomyces cerevisiae MLH1 gene reveals distinct roles for Mlh1p in meiotic crossing over and in vegetative and meiotic mismatch repair

In eukaryotic cells, DNA mismatch repair is initiated by a conserved family of MutS (Msh) and MutL (Mlh) homolog proteins. Mlh1 is unique among Mlh proteins because it is required in mismatch repair and for wild-type levels of crossing over during meiosis. In this study, 60 new alleles of MLH1 were examined for defects in vegetative and meiotic mismatch repair as well as in meiotic crossing over. Four alleles predicted to disrupt the Mlh1p ATPase activity conferred defects in all functions assayed. Three mutations, mlh1-2, -29, and -31, caused defects in mismatch repair during vegetative growth but allowed nearly wild-type levels of meiotic crossing over and spore viability. Surprisingly, these mutants did not accumulate high levels of postmeiotic segregation at the ARG4 recombination hotspot. In biochemical assays, Pms1p failed to copurify with mlh1-2, and two-hybrid studies indicated that this allele did not interact with Pms1p and Mlh3p but maintained wild-type interactions with Exo1p and Sgs1p. mlh1-29 and mlh1-31 did not alter the ability of Mlh1p-Pms1p to form a ternary complex with a mismatch substrate and Msh2p-Msh6p, suggesting that the region mutated in these alleles could be responsible for signaling events that take place after ternary complex formation. These results indicate that mismatches formed during genetic recombination are processed differently than during replication and that, compared to mismatch repair functions, the meiotic crossing-over role of MLH1 appears to be more resistant to mutagenesis, perhaps indicating a structural role for Mlh1p during crossing over.