TRANSLOCATIONS BETWEEN THE X AND THE Y CHROMOSOMES OF DROSOPHILA MELANOGASTER

Abstract

1 NDUCED chromosomal rearrangements in Drosophila have generally been recovered from cells that were in postmeiotic stages, i.e., spermatids and spermatozoa, at the time of treatment. Since the X and the Y chromosomes segregate into separate cells at the first meiotic division, recovery of interchanges between these two elements has therefore been precluded. Induction of X;Y translocations (i.e., T(X;Y)'s) in mature sperm can be accomplished by treating males that carry an extra Y chromosome. These males produce sperm carrying both the X and the Y in one third or more of the cases. PANSHIN (1941 a,b) has recorded recovery of seven reciprocal translocations between the X and the Y from irradiated In(1)wm4/Y/Y males. He reports that the translocations were recognized because T(In(l)wm4;Y)/y w f bb females show less severe variegation than In(l)wm4/y w f bb/Y females. He selected slightly variegated females and recorded as T(X;Y) 's those that produced a viable aneuploid class of progeny. Since these translocations were incidental to the purpose of PANSHIN'S experiments, however, he did not study them further. Translocations between compound X chromosomes and the Y have been induced by irradiation of oocytes and extensively studied by several investigators (PARKER 1953, 1954; MULLER and HERSKOWITZ 1954; ABRAHAMSON, HERS-KOWITZ, and MULLER 1956; PARKER and MCCRONE 1958; PARKER and HAM-MOND 1958). This method, however, leads to the recovery of only half of each induced translocation as a detachment; the other half is included in a polar nucleus during meiosis and therefore lost. Furthermore, detachments are a special sample of X;Y translocations, since the distribution of break points in the X is restricted by the limited degree of aneuploidy that is compatible with recovery of a detachment. It is therefore clear that the oocyte method is not suitable for an exhaustive study of interchange between the X and the Y chromosomes. Rearrangements involving the X chromosome are likely to be associated with recessive lethality (PATTERSON, STONE, BEDICHEK, and SUCHE 1934) or male sterility (SCHULTZ 1947; LINDSLEY, EDINGTON, and VON HALLE 1960) ; rearrangements involving the Y chromosome are likely to be associated with male sterility (NEUHAUS 1939). Consequently, to get an unbiased estimate of involvement of either X or Y in induced rearrangements, the irradiated genome should be recovered in F, females rather than males, as is commonly done. This pre