Determination of Chromosomal Sex ‡

The sex of an individual may be defined in three different ways: a. The type of gonad present b. General anatomical appearance and psychological orientation c. Genetic factors as determined by the presence of the XX or XY chromosomes. If uniformity is absent or equivocal in these characteristics, the decision as to whether an individual should be classified as male or female is difficult and is usually based on the prevailing general anatomical appearance. This may be unsatisfactory and is often misleading. General anatomical appearance and psychological orientation may be susceptible to spontaneous or iatrogenic changes. The chromosomal sex is perhaps closest to the "true" sex and is of greatest importance in the early recognition and treatment of intersexuality. As early as 1917 Weiman,'2 and later Painter,"5 showed that sex chromosomes in the developing human male germ cell tend to remain compact with deep staining properties during the nuclear interphase. This is in contrast to other chromosomes which become so diffuse that it is difficult to identify them. Further, Geitler' demonstrated a sex difference in nuclear morphology in the Gerris lateralis and Gerris lacustris, waterbugs, on the basis of heterochromatic properties of their sex chromosomes. The early investigators in this field have therefore speculated that the fusion of the hetero-chromatic portions of the two X chromosomes in the female would form a mass large enough to be detected by ordinary microscopic means, the small size of the Y chromosome being probably the reason for the minute size of the sex chromatin in male nuclei. It was Barr et al. in 1950"' '> who described for the first time an intranuclear body in the nerve cell of the cat, identified as the female sex chromatin. Large neurons seemed to be best suitable for this work because their nucleus is vesicular and lacks other * Instructor in Obstetrics and Gynecology. t Assistant in Research in Obstetrics and Gynecology.