Heterosis in Cepaea

A test has been made of the association of heterozygosity with shell breadth in the polymorphic snail Cepaea nemoralis. The material was collected by C. B. Goodhart from a series of paired sites at which individuals reached different adult breadths. Dominant phenotypes, in which a large fraction was heterozygous, had a greater breadth and lower variance than recessive phenotypes regardless of whether the measurement was of shell ground colour, banding or the double recessive vs. the rest. Most of the difference was contributed by samples from the habitat where animals reached the largest size. The result is consistent with existence of heterotic sections of chromosome that include the colour and banding loci, and may help to explain the persistence of the polymorphism.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 49–53.     

On the Origin of Mendelian Genetics

SYNOPSIS. An examination of research on heredity in the yearsbetween Mendel's scientific work and his multiple rediscovery(approximately 1850–1900) suggests that at the turn ofthe century the elucidation of the mechanism of the transmissionof hereditary traits from parent to offspring was inevitable.By 1900, a variety of different investigators were either attackingthe problem of genetic transmission directly and successfully,or were examining specific aspects of the issue. However, itappears that the identity of analysis used by Mendel and byhis rediscoverers was primarily the result of the latter allfollowing Mendel's formulation. Had Mendel not been rediscovered,the "Laws of Heredity" would likely have been formulated quitedifferently, and been discovered and refined over a period oftime rather than all being discovered and given their finalform at the very outset.     

Reiteration and Clustering of DNA Sequences Complementary to Histone Messenger RNA

The DNA complements of 9S messenger RNA thought to code for histones in sea urchins are reiterated, closely clustered, relatively stable in evolution and development and potentially separable from other nuclear DNA.     

Growth and Nutrient Status of Quercus rubra L. in Response to Al and Ca

Northern red oak (Quercus rubra L.) seedlings were grown for63 d in a complete nutrient solution (pH 3.8) containing oneof three concentrations of Al (0, 0.75 or 2-0 mol m^–3)and either 10 or 250 mmol m^–3 Ca. Of all solution variables,the In of (Al³⁺)/(Ca²⁺), the solution activities ratio, wasmost closely correlated with declines in shoot and root growth.Ln (Al³⁺)/(Ca²⁺) also most closely predicted leaf and root [Mg],[Al], and [Al]/[Ca]. These three variables in turn were closelyrelated to growth. Toxic levels of (Al³⁺) and (Al³⁺)/(Ca²⁺)in solution are compared to levels in forest soils. Key words: Al phytotoxicity, Al x Ca interaction, Quercus rubra     

Physiological Insights from Cellular and Network Models of the Stomatogastric Nervous System of Lobsters and Crabs

SYNOPSIS. The stomatogastric nervous system of decapod crustaceansis an ideal system for the study of the processes underlyingthe generation of rhythmic movements by the nervous system.In this chapter we review recent work that uses mathematicalanalyses and computer simulations to understand: 1) the roleof individual currents in controlling the activity of neurons,and 2) the effects of electrical coupling on the activity ofneuronal oscillators. The aim of this review is to highlight,for the physiologist, what these studies have taught us aboutthe organization and function of single cell and multicellularneuronal oscillators.     

Changes in a deep lake following sewage diversion – a challenge to the orthodoxy of external phosphorus control as a restoration strategy?

1. The restoration of deep lakes has traditionally focused on reducing the external phosphorus loading. 2. Following the diversion of sewage effluent, that led to marked reductions in nutrient concentrations in its main inflow, Rostherne Mere has shown no reduction in phosphorus or chlorophyll a concentrations. A shallow lake upstream (Little Mere), however, has shown a marked response to effluent diversion. 3. Nutrient budgets for Rostherne Mere reveal that sewage effluent was by far the most significant external source of total phosphorus and that diffuse drainage from the catchment was the most significant external source of dissolved inorganic nitrogen. Phosphorus loads from groundwater and a bird roost were insignificant. Internal sources of phosphorus were, however, considerable and were largely responsible for the observed delay in recovery. 4. Phosphorus limitation of phytoplankton biomass may never be attainable because of substantial internal and diffuse sources of phosphorus, combined with a long retention time. Nitrogen is likely to be more important in limiting phytoplankton biomass. Control of diffuse nitrogen sources may therefore be more effective in the restoration of the deeper lakes of this region.     

Tolerance to the fungal pathogen Rhizoctonia solani AG4 of transgenic tobacco expressing the maize ribosome-inactivating protein b-32

The maize b-32 protein is a functional ribosome-inactivating protein (RIP), inhibiting in vitro translation in the cell-free reticulocyte-derived system and having specific N-glycosidase activity on 28S rRNA. Previous results indicated that opaque-2 (o2) mutant kernels, lacking b-32, show an increased susceptibility to fungal attack and insect feeding and that ectopic expression in plants of a barley and a pokeweed RIP leads to increased tolerance to fungal and viral infection. This prompted us to test whether b-32 might functi on as a protectant against pathogens. The b32.66 cDNA clone under the control of the potato wun1 gene promoter was introduced into tobacco by Agrobacterium tumefaciens-mediated transformation. Out of 23 kanamycin resistant regenerated shoots, 16 contained a PCR fragment of the corrrect size spanning the boundary between the promoter used and the coding region of the b-32 gene. Eight independently transformed tobacco lines were randomly chosen for protein analysis: all of them expressed b-32 protein. The data presented indicate that transgenic tobacco plants expressing b-32 show an increased tolerance against infection by the soil-borne fungal pathogen Rhizoctonia solani Kuhn