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Biomedical subjects

J A Mitchell

Publications and source records attributed to J A Mitchell.

At least 253 records · Page 14Linked to original sources
PubMed1978

Fine structure of the homologous tergo-coxal muscles of flying and flightless beetles.

The flight-related tergo-coxal muscles of flying and flightless beetles are compared. In the flying beetle, Pachynoda sinuata, the myofibrils and cylindrical and the myofilaments packed in double hexagonal arrays. The sarcomeres are short (2.8 micrometer) and wide with many large, closely packed adjacent mitochondria but the sarcoplasmic reticulum is poorly developed in this fibrillar (asynchronous) muscle. Sarcoplasmic glycogen in rosette form is abundant. In the flightless beetle, Anthia thoracica, the myofibrils are lamellar-like with sarcomeres of 5.3 micrometer. The myosin filaments form a single hexagonal array each thick filament having an orbital of 11 to 12 thin filaments. The width of the Z-line (120 nm) of A. thoracia muscle was twice that of the Z-line of P. sinuata muscle. The sarcoplasmic reticulum and T-system are well-developed in this afibrillar (synchronous) muscle. Few glycogen granules are present. Triangular projections of the sarcolemma occur regularly opposite the Z-lines in A. thoracica and they appear to extend into the Z-lines. Membranous connections joint adjacent Z-lines in A. thoracica and occasionally in P. sinuata.

Animals↗
PubMed1977

Fitness effects of EMS-induced mutations on the X chromosome of Drosophila melanogaster. I. Viability effects and heterozygous fitness effects.

Drosophila melanogaster X chromosomes were mutagenized by feeding males sucrose solutions containing ethyl methanesulfonate (EMS); the concentrations of EMS in the food were 2.5 mM, 5.0 mM, and 10.0 mM. Chromosomes were exposed to the mutagen up to three times by treating males in succeeding generations. After treatment, the effective exposures were 2.5, 5.0, 7.5, 10.0, 15.0, and 30.0 mM EMS. X chromosomes treated in this manner were tested for effects on fitness in both hemizygous and heterozygous conditions, and for effects on viability in hemizygous and homozygous conditions. In addition, untreated X chromosomes were available for study. The viability and heterozygous fitness effects are presented in this paper, and the hemizygous fitness effects are discussed in the accompanying one (MITCHELL and SIMMONS 1977). Hemizygous and homozygous viability effects were measured by segregation tests in vial cultures. For hemizygous males, viability was reduced 0.5 percent per mM EMS treatment; for homozygous females, it was reduced 0.7% per mM treatment. The decline in viability appeared to be a linear function of EMS dose. The viabilities of males and females were strongly correlated. Heterozygous fitness effects were measured by monitoring changes in the frequencies of treated and untreated X chromosomes in discrete generation populations which, through the use of an X-Y translocation, maintained them only in heterozygous condition. Flies that were heterozygous for a treated chromosome were found to be 0.4% less fit per mM EMS than flies heterozygous for an untreated one.

Animals↗
PubMed1977

Fitness effects of EMS-induced mutations on the X chromosome of Drosophila melanogaster. II. Hemizygous fitness effects.

X chromosomes mutagenized with EMS were tested for their effects on the fitness of hemizygous carriers. The tests were carried out in populations in which treated and untreated X chromosomes segregated from matings between males and attached-X females; the populations were maintained for several generations, during which time changes in the frequencies of the treated and untreated chromosomes were observed. From the rates at which the frequencies changed, the fitness effects of the treated chromosomes were determined. It was found that flies hemizygous for a mutagenized chromosome were 1.7% less fit per mM EMS treatment than those hemizygous for an untreated chromosome. Since the same flies were only 0.5% per mM less viable than their untreated counterparts, the total fitness effect of an X chromosome carrying EMS-induced mutants is three to four times greater than its viability effect. By comparing the heterozygous effect of a mutagenized X chromosome on fitness with the corresponding hemizygous effect, the dominance value for the chromosome is estimated to be about 0.25.

Animals↗
PubMed1976

Three-dimensional construction tests for children aged five and six years.

The constructional praxis ability of 69 normal 5 and 6 year olds was studied to validate established norms, to gain normative data for the Gesell Block Test and the Benton and Fogel Test of Constructional Praxis, and to identify a developmental continuum. No significant difference was found between scores obtained by the two age groups; however, a difference significant at the less than .05 level was found between scores of five-year-old boys and girls. The results suggest that these tests measure a continuum of development and that with revisions they may be useful to provide additional information about development of constructional praxis ability in a larger sample of normal and brain-damaged children.

Apraxias↗