SEX-LINKED RECESSIVE LETHALS IN DROSOPHILA WHOSE EXPRESSION IS SUPPRESSED BY THE Y CHROMOSOME

Abstract

A method was devised which allows the detection and recovery of sex- linked recessive letheals with lethal phenotype that is suppressed bp the Y chromosome, as well as onthodox lethals that are inviable with or without a Y. With doses of 3 and 4 kr, approximately 20% of all induced sex-linked recessive lethals survive in the presence of a Y chromosome and are consequently overlooked by currently used methods of lethal detection. The Y-suppressed lethals may be divided into two major classes. About one-eighth of them are deficiencies for the proximal heterochromatin, specifically for bb/sup +/, and they are suppressed by the Y because the Y carries the homologous region. The other seven-eighths are nearly all associated with gross rearrangements with at least one break point in the chromocentral heterochromatin and at least ore in the X. These are concluded to be variegated position-effect lethals. The V-type position-effect lethals may be further subdivided into one group that is male fertile and associated with X chromosome inversions or insertional translocations and another group that is male sterile and associated with reciprocal translocations with a break in the X and a break iu the chromocentral heterochronintin of chromasome 2 or 3. Themore » sterility of the reciprocal translocations is attributable to failure of sperm head elongation. It is postulated that continuity of the X chromosome plays an important role in normal spermiogenesis and that this continuity is disrupt by reciprocal translocation. (auth)« less