Synthesis of an attached autosome, C(3)RM, in Drosophila pseudoobscura.

Drosophila pseudoobscura has three acrocentric autosomes. In the experiments reported, homologous arms of the third chromosome were attached to the same centromere. This is a 'reversed metacentric compound' third chromosome, denoted by C(3)RM. This compound chromosome is relatively fertile in within-strain crosses (ca. 50% egg hatch) but sterile when outcrossed to a normal karyotype. When constructing translocations for this experiment, the behavior of the Y-autosome translocations suggested that this species can tolerate more Y chromosome deficiency while retaining fertility than can Drosophila melanogaster. Finally, there were no Robertsonian exchanges observed among the 96 autosome-autosome translocations analyzed cytologically.