In 1949, Canadian anatomist Murray Barr announced the discovery of a peculiar entity in the cell nucleus that was present in females and absent in males. The identity of this entity remained uncertain for a decade even though Barr hypothesised a relationship between it and the sex chromosomes and called it the ‘‘sex chromatin.’’ This hypothesis inspired the development of the chromatin into a technology that could indicate ‘‘chromosomal’’ or ‘‘genetic’’ sex, which supposedly established male and female sex difference as a binary and fundamental characteristic of humans and other animals at conception. Barr collaborated with other researchers and potential patients who applied the sex chromatin test, hoping that it could identify the ‘‘true’’ sex of intersexuals, homosexuals, and transsexuals. Ironically, the application of the test to intersexuals would lead to a revision of the identity of the sex chromatin itself. The history of the sex chromatin illuminates how the significance and essence of this laboratory object evolved with its use as a clinical and research tool. Researchers had hoped that the test would sort the intersex into just two categories, male and female. Instead, the sex chromatin helped to multiply categories of the intersex, distinguished them from inverts, underpinned psychosocial gender as a new dimension of sex difference, and in the process had its own identity refashioned. Today, we call it the Barr body and its story reminds us of the power and limit of biotechnologies to determine who we are.

This article is about the hopes and the uncertainties that people expressed for what the sex chromatin test could do and what it could tell them. It is also about the making of a new technology for diagnosing ‘‘true sex’’ from bodily tissues that were not obviously sexual, like skin or cheek swabs. Initially a serendipitous discovery, the sex chromatin was fashioned into an authoritative, medical tool that could purportedly separate male from female, homosexual from heterosexual, and normal from abnormal. In what follows, I will make three major arguments. First, I will demonstrate how the sex chromatin satisfied social expectations that only two sexes existed. Even if the exact relationship between the sex chromosomes and chromatin remained ambiguous, the presence or absence of the chromatin provided a binary answer to a question presumed to have only two possibilities. Thus, the sex chromatin re-presented the essence of genetic sex. Second, I will argue that the chromatin test helped to erase old sexual identities and create new ones. After the test, inverts became homosexuals and transsexuals, psychological gender emerged as a dimension of difference distinct from biological sex, and two new kinds of intersexuals were minted. Third, in the most ironic twist of all, I will show how these new classes of intersexuals provided evidence that would re-identify the sex chromatin itself. The result was a resolution of a long-standing uncertainty regarding the relationship between the sex chromatin and X chromosomes. Together, these recursive histories of the sex chromatin test demonstrate how social expectations help to constitute an emerging medico-scientific technology, and how that technology can in turn reformulate the cultural expectations that gave it meaning.

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