Ultrastructural changes in sarcosomes after exposure of adult Calliphora erythrocephala to lethal and sub-lethal high temperatures

The effects of lethal and sub-lethal high temperatures on the morphology of intact flight muscle sarcosomes of adult Calliphora erythrocephala are described. Treatment of adult flies to lethal temperatures results in ultrastructural changes in the organisation of the cristae and the appearance of electron opaque inclusions. These changes have not been observed after sub-lethal heat treatment, when 50% of the animals recover. It is suggested that changes in the ultrastructure of the intact sarcosomes may be correlated with changes in their ability to couple oxidative phosphorylation with α-glycerophosphate. Age-dependent changes in the sensitivity of sarcosomes are related to changes in the heat death point of the animal and suggest that the impairment of sarcosomal function may be one of the primary lesions in heat death of adult C. erythrocephala.     

The simulation of multi-neurone networks: Modelling of the lateral inhibition of the eye and the generation of respiratory rhythm

We describe a model of a single neurone, and a method of interconnecting such neurone models suitable for multi-neurone network simulations on a digital computer. Two simulations are described; the lateral inhibition in the eye of the Limulus and the generation of respiratory rhythm in the brain stem of the cat.     

Hyperchromicity and Strand Separation in Bacterial DNA

Studies of the per cent of strand separation of N¹⁴-N¹⁵ hybrid coli DNA heated to various temperatures in formaldehyde have shown that the process of strand separation is a function of temperature and formaldehyde concentration and is directly related to the measured hyperchromicity. No strands separate until about 75 per cent of full hyperchromicity is obtained, and even at apparently full hyperchromicity a large fraction of the strands may be held together, possibly by guanine-cytosine-rich regions.     

The Effects of Central Asymmetry on the Propagation of Palindromic DNA in Bacteriophage λ Are Consistent with Cruciform Extrusion in Vivo

The propagation of λ phages carrying long perfect palindromes has been compared with that of phages carrying imperfect palindromes with small regions of central asymmetry. The perfect palindromes confer a more deleterious phenotype than those with central asymmetry and the severity of the phenotype declines with the length of asymmetry in the range from O to 27 base pairs. These results argue that a center-dependent reaction is involved in the phenotypic effects of palindromic DNA sequences, consistent with the idea that cruciform extrusion occurs in vivo.     

Quantitative measures and 3D shell models reveal interactions between bands and their position on growing snail shells

The nature of shell growth in gastropods is useful because it preserves the ontogeny of shape, colour, and banding patterns, making them an ideal system for understanding how inherited variation develops, is established and maintained within a population. However, qualitative scoring of inherited shell characters means there is a lack of knowledge regarding the mechanisms that control fine variation. Here, we combine empirical measures of quantitative variation and 3D modeling of shells to understand how bands are placed and interact. By comparing five‐banded Cepaea individuals to shells lacking individual bands, we show that individual band absence has minor but significant impacts upon the position of remaining bands, implying that the locus controlling band presence/absence mainly acts after position is established. Then, we show that the shell grows at a similar rate, except for the region below the lowermost band. This demonstrates that wider bands of Cepaea are not an artifact of greater shell growth on the lower shell; they begin wider and grow at the same rate as other bands. Finally, we show that 3D models of shell shape and banding pattern, inferred from 2D photos using ShellShaper software, are congruent with empirical measures. This work therefore establishes a method that may be used for comparative studies of quantitative banding variation in snail shells, extraction of growth parameters, and morphometrics. In the future, studies that link the banding phenotype to the network of shell matrix proteins involved in biomineralization and patterning may ultimately aid in understanding the diversity of shell forms found in molluscs.