Summary

In the opening of this chapter, Mukherjee writes about his mother, who is a twin. He writes about the different paths the sisters' lives have taken as well as the similarities and differences in their personalities. He then transitions into how genes determine and influence sex, gender, and gender identity. Biological sex was discovered to be determined by chromosomes in the early 20th century (XY for men, XX for women). Mukherjee then discusses cases in which biological sex does not adhere to the typical binaries determined by chromosomes. He explains Swyer syndrome, in which anatomically and physiologically female people possess XY chromosomes.

Mukherjee then discusses the impact of genes on gender identity. Through several case studies, he demonstrates that gender identity cannot be "created or programmed [...] by training, suggestion, behavioral enforcement, social performance, or cultural interventions" (366). Based on...