A model and lexicon for pollen fate

As pollination biology undergoes unprecedented growth as a discipline, confusion in the use of terms has become increasingly common. The need for a flexible yet unambiguous terminology has become urgent. As an example we discuss how the term “pollination efficiency” is used differently by 18 studies, and “pollinator effectiveness” by seven others. Here we present flowcharts of two general models of pollination systems (biotic and abiotic) that trace all the events from pollen production to development of seed or fruit, and we develop a lexicon for the quantities of pollen, processes of transfers (to a vector, to a stigma), and ratios of quantities that are of interest in studies of pollination and mating systems. An appendix includes a glossary of the definitions we suggest.     

Transfer of Ph I genes promoting homoeologous pairing from Triticum speltoides to common wheat

Diploid-like chromosome pairing in polyploid wheat is controlled by several Ph (pairing homoeologous) genes with major and minor effects. Homoeologous pairing occurs in either the absence of these genes or their inhibition by genes from other species (Ph ^I genes). We transferred Ph ^I genes from Triticum speltoides (syn Aegilops speltoides) to T. aestivum, and on the basis of further analysis it appears that two duplicate and independent Ph ^I genes were transferred. Since Ph ^I genes are epistatic to the Ph genes of wheat, homoeologous pairing between the wheat and alien chromosomes occurs in the F₁ hybrids. Using the Ph ^I gene stock, we could demonstrate homoeologous pairing between the wheat and Haynaldia villosa chromosomes. Since homoeologous pairing occurs in F₁ hybrids and no cytogenetic manipulation is needed, the Ph ^I gene stock may be a versatile tool for effecting rapid and efficient alien genetic transfers to wheat.Contribution no. 93-435-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506-5502, USA     

Genetic mapping of 14 short tandem repeat polymorphisms on human chromosome 22

We have constructed a linkage map of 14 short tandem repeat polymorphisms (11 with heterozygosity > 70%) on the long arm of human chromosome 22 using 23 non-CEPH pedigrees. Twelve of the markers could be positioned uniquely with a likelihood of at least 1,000:1, and distributed at an average distance of 6.62 cM (range 1.5–16.1 cM). The sex-combined map covers a total of 79.6 cM, the female map 93.2 cM and the male map 64.6 cM. Based on comparisons between physical maps and other genetic maps, we estimate that our map covers 70%–80% of the chromosome. The map integrates markers from previous genetic maps and uniquely positions one marker (D22S307). Data from physical mapping on the location of four genetic markers correlates well with our linkage map, and provides information on an additional marker (D22S315). This map will facilitate high resolution mapping of additional polymorphic loci and disease genes on chromosome 22, and act as a reference for building and verifying physical maps.     

Conservation of motifs within the unusually variable polypeptide sequences of type I restriction and modification enzymes

Type I restriction enzymes comprise three subunits encoded by genes designated hsdR, hsdM, and hsdS; S confers sequence specificity. Three families of enzymes are known and within families, but not between, hsdM and hsdR are conserved. Consequently, interfamily comparisons of M and R sequences focus on regions of putative functional significance, while both inter- and intrafamily comparisons address the origin, nature and role of diversity of type I restriction systems. We have determined the sequence of the hsdR gene for EcoA, thus making available sequences of all three hsd genes of one representative from each family. The predicted R polypeptide sequences share conserved regions with one superfamily of putative helicases, so-called ‘DEAD box’ proteins; these conserved sequences may be associated with the ATP-dependent translocation of DNA that precedes restriction. We also present hsdM and hsdR sequences for EcoE, a member of the same family as EcoA. The sequences of the M and R genes of EcoA and EcoE are at least as divergent as typical genes from Escherichia coli and Salmonella, perhaps as the result of selection favouring diversity of restriction specificities combined with lateral transfer among different species.     

Clinical and epidemiologic characteristics of hepatitis C in a gastroenterology/hepatology practice in Ottawa.

OBJECTIVE: To examine the clinical and epidemiologic features of hepatitis C virus (HCV) infection in a gastroenterology/hepatology practice in Ottawa. DESIGN: Retrospective chart review. PATIENTS: Sixty-three consecutive patients found to be anti-HCV positive. Their charts were analysed with respect to risk factors, history of hepatitis, serum aspartate aminotransferase (AST) levels and the presence of hepatitis B markers. The long-term sexual partners of 29 patients agreed to undergo HCV antibody testing. RESULTS: Of the patients 48 (76%) had been exposed to HCV parenterally: 27 used intravenous drugs, and 21 had received blood or blood products. Eleven patients did not have any known risk factor (sporadic infection), but eight of them had lived in countries where hepatitis C may be more prevalent; the other three had locally acquired infection. The mean serum AST level at the first visit was 140 (normally less than 40) IU/L. At least one hepatitis B marker was identified in 33% of the patients. None of the sexual partners who were tested were anti-HCV positive. CONCLUSION: Most cases of hepatitis C in Ottawa are acquired through parenteral exposure; sexual transmission is rare. Sporadic infection in the Ottawa region is rare but may be more common in people from countries with a higher prevalence rate of hepatitis C. Most cases of hepatitis C are asymptomatic.     

Constraints on prey size selection by the three-spined stickleback: energy requirements and the capacity and fullness of the gut

An experiment was designed to study how gut fullness and encounter with 5-mm Asellus aquaticus influenced acceptance or rejection of less profitable 8-mm Asellus . 45-mm sticklebacks were found to always accept 5-mm prey whereas 8-mm prey were accepted with an initial probability of about 0.9. This probability decreased as the gut filled. Fish of differing sizes and sex had similar daily energy intakes per unit body size, however the acceptance of 8-mm prey was related to fish size. Whenever a fish orientated to a prey it was followed by pursuit and manipulation independently of prey size. The decision to accept or reject prey occurred after one manipulation, a criterion that was more variable for the larger prey. For one feeding session per day the total energy intake was almost constant despite the changing combination of prey sizes eaten. The fish ate prey with long handling times if the energetic contents of the stomach had not reached 450 J. Calculations were made of how many of each millimetre prey size group would satisfy the 450 J demand and how long the estimated number would take to handle. This showed that the best option is to consume 5-mm prey if given the choice.     

Actin-related protein 1 and cytoplasmic dynein-based motility - what's the connection?

The actin-related protein Arp1 works in conjunction with the microtubule-based motor cytoplasmic dynein to drive many types of intracellular motility. In vertebrate cells, Arp1 is present exclusively in the form of a 37-nm filament that constitutes the backbone of dynactin, a 1.2-MDa macromolecular complex containing nine other polypeptides. Dynactin has been proposed to function as the link between dynein and its cargo. Recent work indicates that the dynactin subunit p150(Glued) mediates the interaction of the dynactin molecule with dynein and microtubules, leaving the Arp1 filament as a possible cargo-binding domain. Mechanisms for binding of F-actin to membranes are discussed as models of the Arp1-membrane interaction.     

Effect of doctors' ethnicity and country of qualification on prescribing patterns in single handed general practices: linkage of information collected by questionnaire and from routine data.

OBJECTIVES: To test whether Asian general practitioners who qualified in the Indian subcontinent prescribe items more often, more expensive items, and fewer generic drugs than their British trained Asian and non-Asian counterparts. DESIGN: Linkage study using data collected by questionnaire and from routine sources. SETTING: General practices in England. SUBJECTS: 155 single handed general practitioners: 42 Asian doctors qualified in United Kingdom (group 1), 58 white doctors qualified in United Kingdom (group 2), and 55 Asian doctors qualified in Indian subcontinent (group 3). MAIN OUTCOME MEASURES: Prescribing cost (cost per ASTRO-PU), prescribing frequency (number of items per ASTRO-PU), and generic prescribing (percentage of drugs prescribed that are generic). RESULTS: Doctors in group 1 were significantly younger than those in the other groups and had a higher proportion of patients who were from deprived wards. There was no difference between the groups in the proportion of female doctors and total list size. After adjustment for confounding factors, there were no significant differences between the three groups for prescribing cost (16.58 (95% confidence interval 6.39 to 26.77) for group 1, 17.31 (6.92 to 27.69) for group 2, 17.80 (7.22 to 28.38) for group 3, P = 0.55); prescribing frequency (6.58 (4.60 to 8.40), 6.45 (4.70 to 8.30), 7.89 (6.16 to 9.64), P = 0.34); and generic prescribing (44.44 (38.95 to 49.93), 47.41 (42.12 to 52.70), 44.04 (38.75 to 49.33), P = 0.37). CONCLUSIONS: Asian doctors qualified from the Indian subcontinent did not differ from British trained doctors in their prescribing practice. This study refutes the common belief that Asian doctors are high volume and high cost prescribers.     

Molecular-genetic maps for group 1 chromosomes of Triticeae species and their relation to chromosomes in rice and oat

Group 1 chromosomes of the Triticeae tribe have been studied extensively because many important genes have been assigned to them. In this paper, chromosome 1 linkage maps of Triticum aestivum, T. tauschii, and T. monococcum are compared with existing barley and rye maps to develop a consensus map for Triticeae species and thus facilitate the mapping of agronomic genes in this tribe. The consensus map that was developed consists of 14 agronomically important genes, 17 DNA markers that were derived from known-function clones, and 76 DNA markers derived from anonymous clones. There are 12 inconsistencies in the order of markers among seven wheat, four barley, and two rye maps. A comparison of the Triticeae group 1 chromosome consensus map with linkage maps of homoeologous chromosomes in rice indicates that the linkage maps for the long arm and the proximal portion of the short arm of group 1 chromosomes are conserved among these species. Similarly, gene order is conserved between Triticeae chromosome 1 and its homoeologous chromosome in oat. The location of the centromere in rice and oat chromosomes is estimated from its position in homoeologous group 1 chromosomes of Triticeae.