Length variation and secondary structure of introns in the Mlc1 gene in six species of Drosophila

A nearly universal feature of intron sequences is that even closely related species exhibit a large number of insertion/deletion differences. The goal of the analysis described here is to test whether the observed pattern of insertion/deletion events in the genealogy of the myosin alkali light chain (Mlc1) gene is consistent with neutrality, and if not, to determine the underlying forces of evolutionary change. Mlc1 pre-mRNA is alternatively spliced, and one constraint is that signals necessary for tissue-specificity of directed splicing must be conserved. If the total length of an intron is functionally constrained, then the distribution of indels on branches of the gene genealogy should reflect a departure from randomness. Here we perform a phylogenetic analysis, inferring ancestral states wherever possible on a phylogeny of 29 alleles of Mlc1 from six species of Drosophila. Observed patterns of indels on the genealogy were compared to those from simulated data, with the result that we cannot reject the null hypothesis of neutrality. A clear departure from a neutral prediction was seen in the excess folding free energy predicted for the introns flanking the alternatively spliced exon. Relative rate tests also suggest a retardation in the rate of Mlc1 sequence evolution in the simulans clade.      

Effects of long-term fixation on histological quality of undecalcified murine bones embedded in methylmethacrylate.

While long-term fixation and storage of specimens is common and useful for many research projects, it is particularly important for space flight investigations where samples may not be returned to Earth for several months (International Space Station) or years (manned mission to Mars). We examined two critical challenges of space flight experimentation: the effect of long-term fixation on the quality of mouse bone preservation and the preservation of antigens and enzymes for both histochemical and immunohistochemical analyses, and how the animal/sample processing affects the preservation. We show that long-term fixation minimally affects standard histological staining, but that enzyme histochemistry and immunolabeling are greatly compromised. Further, we demonstrate that whole animal preservation is not as suitable as whole leg or stripped leg preservation for long-term fixation and all histological analyses. Overall, we recommend whole leg processing for long-term storage of bone specimens in fixative prior to embedding in plastic for histological examination.     

Selection for carcass quality in hill sheep measured by X-ray computer tomography

This paper describes an investigation of the use of computer tomography (CT) to genetically improve carcass composition and conformation in Scottish Blackface sheep. After 5 years of selection on an index designed to improve both composition and conformation (the 'CT index'), a large response was observed in the CT index, with genetic progress equivalent to 0.11 phenotypic standard deviations per year. Heritabilities for the index and for the component traits of average CT-assessed muscle area, ultrasonic muscle depth and ultrasonic fat depth were 0.41 (s.e. 0.08), 0.38 (s.e. 0.07), 0.41 (s.e. 0.05) and 0.30 (s.e. 0.05), respectively. The index was positively genetically correlated with ultrasonic muscle depth and carcass weight and negatively genetically correlated with fat class. The genetic and phenotypic correlations among ultrasonic measurements were positive and moderate. However, many of the genetic correlations tended to have large standard errors. Selection on the CT index moderately improved conformation and was successful at decreasing fat class of the carcass. Equivalent selection on live weight at ultrasound scanning would improve carcass and slaughter weight, and total price received, but would have a slightly deleterious impact on conformation score. The results of this study demonstrate that genetic improvement of carcass quality can be achieved in hill sheep using CT assessed traits.     

Laboratory Studies Bearing on Pigment Pattern Polymorphisms in Wild Populations of RANA PIPIENS

Data are presented for 2,393 progeny from a number of crosses related to a study in ecological genetics of the Burnsi and Kandiyohi polymorphisms in natural populations of the leopard frog, Rana pipiens. No significant differences in viability were found between wild-type homozygotes (+/+) and Burnsi heterozygotes (B/+) or homozygotes (B/B). Similarly, no difference in viability was found between wild-type (+/+) and Kandiyohi heterozygotes (K/+) and homozygotes (K/K). However, there appears to be slight reduction in viability of the double dominant heterozygote (B/+; K/+) in comparison with (+/+), (B/+), and (K/+) progeny from the same cross.-The Kandiyohi heterozygotes (K/+) appeared to have a more rapid rate of development from fertilization through metamorphosis than wild-type (+/+) or Burnsi (B+/) or Burnsi-Kandiyohi heterozygotes (B+K/+). Since Kandiyohi is associated primarily with the prairie habitat (Merrell 1965), this finding suggests that the adaptive advantage of Kandiyohi lies in the more rapid rate of development of frogs carrying this gene, enabling them to complete metamorphosis before the prairie breeding ponds dry up.-Data are presented from crosses involving dorsal spot number. The results suggest that heredity plays a role in the determination of dorsal spot number but that non-genetic influences are also of considerable importance.-The results of these crosses are discussed with respect to their bearing on the formation of pigment patterns in Rana pipiens. From the available data it is clear that the pigment pattern in Rana pipiens is a complex trait influenced by major gene loci, by modifying genes, and by environmental effects. The relative importance of these factors varies depending on the particular combination of genetic and environmental conditions.     

Chromosomal Analysis of Ddt-Resistance in a Long-Term Selected Population of DROSOPHILA MELANOGASTER

The genetic basis of DDT-resistance was studied in a population of Drosophila melanogaster. This population was unique in that it had been continually selected for DDT-resistance since 1952 and had achieved a very high level of resistance. The genetic basis of resistance was studied by means of a chromosomal analysis. Fifteen combinations of resistant and control chromosomes were tested using a time-based DDT test. The analysis of the data showed that resistance was multifactorial with each of the three major chromosomes involved. Dominant and recessive second and third chromosome effects were found to be much more important than those of the first chromosome, which had no detectable recessive effects. Second and third chromosome resistance genes showed incomplete dominance. The average dominance of the second chromosome was much less than that of the third chromosome. These large-scale differences between chromosomes' effects and average dominance may indicate that a small number of resistance genes are involved. Two significant interactions between chromosomes were found. Scaling difficulties make the interactions difficult to interpret without further data. It seems possible that positive interactions between resistance have been developed by the long-term directional selection in this population.     

Role of cryptic genes in microbial evolution

Cryptic genes are phenotypically silent DNA sequences, not normally expressed during the life cycle of an individual. They may, however, be activated in a few individuals of a large population by mutation, recombination, insertion elements, or other genetic mechanisms. A consideration of the microbial literature concerning biochemical evolution, physiology, and taxonomy provides the basis for a hypothesis of microbial adaptation and evolution by mutational activation of cryptic genes. Evidence is presented, and a mathematical model is derived, indicating that powerful and biologically important mechanisms exist to prevent the loss of cryptic genes. We propose that cryptic genes persist as a vital element of the genetic repertoire, ready for recall by mutational activation in future generations. Cryptic genes provide a versatile endogenous genetic reservoir that enhances the adaptive potential of a species by a mechanism that is independent of genetic exchange.      

RESULTS OF IRRADIATION IN CANCER OF THE LIP,TONGUE AND EAR

Cancer of the lip: The primary lesion can be controlled by irradiation in approximately 80 per cent of cases. For lesions with metastases there is only about a 25 per cent chance of five-year arrest (irradiation of the primary lesion followed by excision of involved nodes).Cancer of the tongue: Lesions in the anterior two-thirds are controllable by irradiation in about 50 per cent of cases if the nodes are not involved; the salvage is only about 15 per cent if the nodes are involved (nodes treated surgically). Lesions in the posterior third of the tongue are seldom controlled in the author''s experience.Cancer of the ear (auricle): Five-year arrest of basal-cell lesions should be attained by irradiation in about 80 per cent of cases; of squamous-cell lesions in about 60 per cent. If the lesion is extensive, radiation does not offer a superior cosmetic result to operation and entails danger of late chondronecrosis. Therefore extensive lesions are probably best treated surgically. In either event, it appears probable that results of irradiation can be improved by the use of more adequate fields and greater fractionation.     

Morphological and cell association characteristics of Rochalimaea quintana: comparison of the Vole and Fuller strains.

The vole and Fuller strains of Rochalimaea quintana were grown on monolayers of mouse L cells irradiated 7 days previously and examined by light microscopy and scanning and transmission electron microscopy. Most of the bacteria of both strains were shown to adhere to the L cells but remained in an extracellular location. Cell division was frequently seen among the extracellular bacteria. The few intracellular bacteria seemed to be within vacuoles and did not multiply. Attachment to the eucaryotic cell did not seem to involve pili or other bacterial surface structures. The dimensions of the bacteria were approximately 0.45 micron in width by 1.0 to 1.7 micron in length. The cell envelope consisted of the usual trilaminar cell wall and plasma membranes separated by a layer of low electron density, as found in other gram-negative bacteria. No significant differences between the vole and Fuller strains either in morphology or relationship to eucaryotic cells were encountered.     

MATING PREFERENCE AND ITS RELEVANCE TO ADAPTATION IN DROSOPHILA MELANOGASTER: INVERSION POLYMORPHISM AND DDT RESISTANCE

The importance of adult mating success as a component of fitness influencing inversion polymorphism in two DDT-resistant populations of Drosophila melanogaster was investigated. The polymorphism involved In(3R)P and the Standard (St) gene arrangement. In population 731R the St/St females showed greater mating propensity than In/In females, while in population J2 the In/In females showed a significant positive association between mating propensity and the percentage of St/St males present. Mating preference data showed that St/St males were selectively favored over In/In males in both populations. No differences were observed between St/St and St/In karyotypes in either population. Frequency-dependent mating in the form of a rare male mating disadvantage for the In/In males tested against the St/St males in 731R was observed; the St/St males in this case showed a marginally significant rare male mating advantage. Thus, mating success as well as previously measured fecundity and fertility all indicate a selective advantage of the St chromosome over the In chromosome in both populations. This fitness relationship does not predict the equilibrium condition of 70–80% St/In, 20–30% In/In, and 0–10% St/St found in the DDT environment, whereas previously collected larval viability data and estimated adult survivorship do. In at least one population (731R), the adult mating success data do predict the dynamics of the polymorphism in the absence of DDT, whereas viability does not. These results, although limited to two populations under two environments (presence or absence of DDT), suggest that the relationship between adaptation to the environment under study and various components of fitness needs to be investigated fully before assessing which fitness components are most important in determining the effects of natural selection in specific populations.