title: Evaluation and re-evaluation of genetic radiation hazards in man. II. The arm number hypothesis and the induction of reciprocal translocations in man.
abstract: The arm number hypothesis proposed by Brewen and collagues in 1973 has been examined in the light of information thus far available from mammalian studies. In experiments with peripheral blood lymphocytes (radiation in vitro), a linear relationship between dicentric yield and the effective chromosome arm number of the species was obtained in the mouse, Chinese hamster, goat, sheep, pig, wallaby and man. However, the data are not  consistent with such a relationship in several primate species (marmoset, rhesus monkey, cynomolgus monkey, squirrel monkey and the slow loris), the cat and the dog. In the rabbit, the data are conflicting. In the mouse and Chinese hamster the frequencies of reciprocal translocations recorded in spermatocytes descended from irradiated spermatogonia are in line with the expectation based on the arm number hypothesis, whereas in the golden hamster, rabbit and the rhesus monkey they are not. In man and the marmoset, the limited data are not inconsistent with a 2-fold higher sensitivity of these species relative to the mouse although they do not rule out a difference as high as 4-fold. In the guinea-pig, the situation is unclear. New data on the transmission of reciprocal translocations in mice suggest that the frequency in the F1 progeny may be close to one-quarter of that recorded in the spermatocytes of the irradiated fathers (spermatogonial irradiation) at an exposure level of 150 R, whereas at higher exposures, the reduction factor is about one-eighth, the latter being in line with the earlier finding. All these results taken together suggest that inter-specific extrapolation from the radiosensitivity of somatic cells (to dicentric induction) to that of germ cells (to translocation induction) is fraught with uncertainity at present. Certain aspects that need to be studied in more detail in the context of induced chromosome aberrations are discussed.
mesh_terms: D000818:Animals; D002415:Cats; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000528:radiation effects*; D006224:Cricetinae; D004285:Dogs; D006041:Goats; D000882:Haplorhini; D006801:Humans; D007614:Macropodidae; D051379:Mice; D011817:Rabbits; D011831:Radiation Genetics; D011839:Radiation, Ionizing; D012756:Sheep; D013045:Species Specificity; D013552:Swine; D014178:Translocation, Genetic