title: The effect of exposure fractionation on the yield of nondisjunctional segregation involving compound X and free 4-chromosomes in Drosophila.
abstract: This paper describes the effect of fractionation of an exposure of 2000-R X-rays into two 1000-R exposures separated by a 3-h interval on the frequency of various segregation products following chromatoid interchange between a compound X and the 4th chromosome. It was observed that fractionation leads to a decrease of all exceptional progeny, the result being significant at the 0.05-probability level for both classes of detachments; i.e., with or without a 4th chromosome. The finding that the same effect of fractionation was observed for numerical aberration (non-disjunction) and detachment supports the idea that these reflect different consequences of the same primary effect, radiation-induced rearrangement. Furthermore, alternative recoveries were observed to occur at equal frequencies. Following C(1)-4 interchange, the univalent 4 does not segregate at random, but assorts apart from its homologue 1.5 as frequently as it moves to the same pole.
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000528:radiation effects*; D003434:Crossing Over, Genetic / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004330:Drosophila / Q000235:genetics*; D005260:Female; D012854:Sister Chromatid Exchange / Q000528:radiation effects*; D014960:X Chromosome / Q000528:radiation effects; D014965:X-Rays