The Effect of Autosomal Inversions on Crossing over in the X-Chromosome of Drosophila Melanogaster.

HE first evidence of a crossover suppressor was found in 1913 by T STURTEVANT. In 1921 STURTEVANT found the first definite evidence of an inversion when he showed that several third chromosome genes in Drosophila melanogaster were arranged in an inverted order with respect to similar genes in the third chromosome of D. simulans. At this time STURTEVANT predicted that a heterozygous inversion would suppress crossing over and suggested that the Nova Scotia stock (STURTEVANT 1917 and 1919) had an inversion. It was not until 1926, however, that it was actually demonstrated that in a t least one case crossover suppression was due to an inversion (STURTEVANT 1926). The sole effect on crossing over ascribed to inversions until recently is that the number of recovered crossovers is reduced in the chromosome in which the inversion is located. But as long ago as 1919, STURTEVANT suspected that crossover suppressors (inversions) might have an interchromosomal effect. He reported that a high value for crossing over between black and purple was due, in part at least, to a dominant gene (really an inversion) in the third chromosome, which when heterozygous reduced crossing over in this chromosome. WARD (1923) tested the effect of the curly inversion on crossing over in the first and third chromosomes; her observations on crossing over were of no value because of the small number of flies used, but she did notice an increase in multiple crossovers. PAYNE (1924) tested the effect of the Payne inversion on crossing over in the first and second chromosomes. While he counted large numbers of flies, the chromosomes were poorly marked (wem on the first chromosome and b pr c sp on the second) and he ran no controls; he therefore noticed no interchromosomal effect on crossing over. PAYNE made no statement in regard to the number of multiple crossovers recovered. The problem rested here until 1932, when SCHULTZ and REDFIELD (MORGAN, BRIDGES and SCHULTZ 1932) stated that inversions in the first and second chromosomes increased crossing over in the third chromosome. In the following year they published a short account (MORGAN, BRIDGES