FILICIDAL RING-Y CHROMOSOMES IN D. MELANOGASTER

Ring-Y chromosomes are recovered infrequently from crosses of ring-Y-bearing males to females of certain strains (Oster 1964). Experiments described here have unveiled a diverse class of genes that exert a maternal effect on the behavior during cleavage of these "filicidal" ring chromosomes. Cytological observations of inviable embryos have revealed that the ring-Y chromosome causes gross disorganization of the cleavage nuclei. This inviability may be equivalent to the "dominant lethality" attributed to unstable ring-X chromosomes (Hinton 1955; Pasztor 1971). Mapping studies indicate that no single region of the normal Y is solely responsible for the unusual behavior of ring-Y chromosomes.