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A H Sparrow

Publications and source records attributed to A H Sparrow.

At least 19 recordsLinked to original sources
PubMed1976

Comparison of X-ray and gamma-ray dose-response curves for pink somatic mutations in Tradescantia clone 02.

Microdosimetric data indicate that the mean specific energy, eta, produced by individual charged particles from X-rays and gamma rays is different for the two radiation qualities by nearly a factor of two. In order to test whether this influences the initial, linear component in the dose-effect relations, a comparison was made between dose-response curves for pink somatic mutations in Tradescantia clone 02 stamen hairs following X and gamma irradiations. Absorbed doses ranged from 2.66 to 300 rad.The results are in agreement with predictions made on the basis of microdosimetric data. At low doses gamma rays are substantially less effective than X-rays. The RBE of gamma rays vs. X-rays at low doses was approximately 0.6, a value lower than those usually reported in other experimental systems.

Cesium Radioisotopes↗
PubMed1976

Evolution of genome size by DNA doublings.

Logarithmic distributions of nucleic acid contents per genome of species within major phylogenetic groups of organisms tend to form several peaks. These peaks appear to represent intragroup doublings of DNA or RNA which, in the case of eukaryotes, are independent of polyploidy. This phenomenon has been termed cryptopolyploidy. There are numerical similarities in peak values for different taxonomic groups. A high degree of order is suggested when minimum values for the major phylogenetic groups are plotted against a series of theoretical doublings. These data demonstrate the apparent existence of an exponential periodicity over eight orders of magnitude, leading us to suggest an evolutionary continuity of doublings of a basic ancestral genome (of about 300 nucleotides), these doublings being independent of both chromosome number and ploidy level. This proposed continuity encompasses most major life forms and is generally concomitant with increasing evolutionary complexity, particularly in the prokaryotes and lower eukaryotes. Our interpretation of the data presented here must currently be viewed as speculative, and we do not propose that genome doubling is the only mechanism for genome evolution. However, we feel that the evidence is sufficient to warrant serious scrutiny of our proposals. We hope that this approach to a synthesis of available data will provoke discussion and will stimulate further work toward either supporting, modifying, or disproving our hypothesis.

Animals↗
PubMed1975

Chromosomes and cellular radiosensitivity. IV. A new radiotaxon represented by the ferns.

Survival curves were constructed and D0 values determined after X-irradiation of single-celled germinating spores of 14 species of ferns, which had a wide variation in interphase chromosome and nuclear volumes and in DNA content per chromosome and per nucleus. A good fit to a line of slope equal to -1 is given on a log-log plot relating D0 to interphase chromosome volume. In a previous publication (Sparrow, Underbrink and Sparrow 1967), ferns fell into radiotaxon VIII, but the new data suggest that they should be assigned to a new group (VIIa) falling midway between radiotaxa VII and VIII. The calculated energy absorption per chromosome at D0 for VIIa is also intermediate between those for VII and VIII. If the value of this parameter is set at 1 for radiotaxon V, that for VIIa is approximately 32 times greater and the radiotaxa V, VI, VII and VIIa form a series 1 : 4 : 14 : 32. The new results indicate that radiotaxon VIII may have to be abandoned unless some other radiobiologically unexplored group (e.g. algae) fills the gap.

Cell Survival↗
PubMed1975

An elusive factor affecting mutation frequency in Tradescantia stamen hairs: its influence on r.b.e.

A comparison of data from several experiments designed to determine either relative biological effectiveness (r.b.e.) or oxygen-enhancement ratios (o.e.r.) as a function of neutron energy revealed a puzzling variability in mutational response for pink mutations in Tradescantia stamen hairs. For some reason that we cannot determine, when the exposure fixtures and accompanying experimental procedures were changed as necessitated by the two studies, the expected mutation frequencies changed for X-rays and for four neutron energies. The other four neutron energies gave the expected results. As a consequence of these changes in mutation frequencies, the magnitude of r.b.e. values changed as well as the relationship of r.b.e. to neutron energy. Consequently, when r.b.e. values were determined using a closed but aerated exposure fixture instead of exposures made in free air, the resulting r.b.e. versus neutron-energy curve more closely paralleled that found by others for the inhibiton of root growth in Vicia faba.

Dose-Response Relationship, Radiation↗
PubMed1972

Mutations induced in Tradescantia by small doses of x-rays and neutrons: analysis of dose-Response curves.

Dose-response curves for pink somatic mutations in Tradescantia stamen hairs were analyzed after neutron and x-ray irradiation with doses ranging from a fraction of a rad to the region of saturation. The dose-effect relation for neutrons indicates a linear dependence from 0.01 to 8 rads; between 0.25 and 5 rads a linear dependence is indicated for x-rays also. As a consequence the relative biological effectiveness reaches a constant value (about 50) at low doses. The observations are in good agreement with the predictions of the theory of dual radiation action and support its interpretation of the effects of radiation on higher organisms. The doubling dose of x-rays was found to be nearly I rad.

Mathematics↗