Spermatogonial crossing over in Drosophila melanogaster and Drosophila ananassae.

FRIESEN (1936) induced crossing over in Drosophila males by X rays and found that most of the exchanges were in a preferred region, the complementary crossover classes were very unequal, and the percent recombination varied greatly from individual to individual. According to him, the data 'were sufficient to demonstrate the occurrence of spermatogonial crossing over. WHITTINGHILL (1937) found that induced crossing over in Drosophila males differs from normal female crossing over in that, in the former it occurred in a preferred region, double and multiple crossover classes were rare, and the complementary crossover classes were unequal. COOPER (1946) observed similarities in induced crossing over and the oogonial disjunction of attached-X chromosomes. This led him to conclude that the induced crossovers were spermatogonial in origin. WHITTINGHILL (1947) reported that in D. melanogaster the presence of Curly inversions heterozygous for rucuca had no effect upon induced crossing over in males. This lack of interchromosomal effect was consistent with the lack of any effect upon the rare disjunction of attached-X chromosomes which is at least sometimes oogonial. WHITTINGHILL (1955) induced crossing over in males heterozygous for a chromosome of standard sequence and a Curly inversion chromosome carrying lethals. The correlated recoveries of only one crossover chromosome and a lethal-free noncrossover chromosome established the occurrence of crossing over long before meiosis, which might have resulted in the death of the sister cell carrying a lethal borne on the noncrossover chromosome and another crossover chromosome. LINDSLEY (1955) gave evidence for the occurrence of spontaneous spermatogonial exchanges between the X and the Y chromosomes. MORIWAKI (1936) reported induced crossing over in early pupae of D. ananassae. Occurrence of radiation induced spermatogonial crossing over has been reported by several workers (CHANDLEY 1962; SAVHAGEN 1961 ; OLIVIERI and OLIVIERI 1963, 1964; FAHMY and FAHMY 1964). In almost all these experiments adult males were treated, where the population of spermatocytes dominates over that of spermatogonia. Moreover the main criterion utilized to distinguish the spermatogonoial crossovers from the meiotic ones is the time of their appearance in the testcross progeny, which may have meiotic crossovers also. This screening is not always easy because in some particular broods a mixture of both these types of crossovers may be obtained ( FAHMY and FAHMY 1964).