EXPERIMENTAL TRANSFER OF MATERNALLY INHERITED ABNORMAL SEX-RATIO IN DROSOPHILA WILLISTONI

Abstract

N previous communications (MALOGOLOWKIN and POULSON 1957; MALOGO-I LOWKIN 1958) a cytoplasmically inherited sex-ratio condition has been described in Drosophila willistoni and in D. paulistorum. In both species, certain females produce progenies consisting mostly or only of daughters. This capacity for the production of unisexual broods is inherited by their entire female progenies and is not transmitted at all by the few exceptional male descendants that appear in some cultures. Many of the eggs deposited by sex-ratio females of D. willistoni are recognizably abnormal within two to four hours of oviposition; and there are reasons to suppose that these dying eggs represent the male zygotes, i.e. eggs fertilized by Y-bearing spermatozoa (MALOGOLOWKIN and POULSON 1957). Although the sex-ratio condition is due to the nonchromosomal transmission of a causative agent, through the cytoplasm of the egg, it is not wholly independent of the influence of chromosomal genes. Crossing of sex-ratio females to males from strains of certain geographic origins results, after a few generations , in an irreversible loss of the sex-ratio condition (MALOGOLOWKIN 1958). These strains evidently contain genes which are less favorable for the multiplication of the causative agent in the cytoplasm than are the genes of many other strains. The present article reports in detail the results of experiments which demonstrate that the causative agent of the sex-ratio condition may be mechanically introduced into the germinal materials of females of previously normal strains. Thus a female of D. willistoni may deposit the sex-ratio type of abnormal, invi-able eggs within about ten days after the injection into her abdomen of ooplasm from an abnormal egg of a sex-ratio female. Moreover, at least a portion of the female progenies of such females carry the causative agent of the sex-ratio condition in their eggs, and the condition is inherited through the female lines from there on with same persistency and regularity as in the original sex-ratio lines of females. MATERIALS AND METHODS The sex-ratio, or unisexual, strains used in the present investigation are those reported on by MALOGOLOWKIN and POULSON (1957) and genetically analyzed by MALOGOLOWKIN (1958). They are derived from a fly collection at Bath, Jamaica, by DRS. W. B. HEED and M. WASSERMAN of the University of Texas. Permanent address: Faculdade Nacional de Filosofia, Universidade do Brazil, Rio de Janeiro.