Programs in bioinformatics, offered in many academic institutes, are assumed to expand women's representation in computer science (CS). Women's enrolment in these programs is high. Our questions are: Do these programs attract different women from those attracted to CS programs? What factors underlie women's decision to enroll in bioinformatics programs? How do these factors differ from those of women who choose CS, if at all? What career opportunities do these women anticipate and pursue? Using questionnaires and interviews, we found a statistically significant difference between the factors that motivate women to choose bioinformatics and others to study CS. Many bioinformatics students did not consider CS as an alternative. Post-facto they learned to love computing, albeit with a biology-oriented purpose. "Computing with purpose" underlies many participants' pursuit of careers in research, CS, and bio-tech. We thus conclude that bioinformatics programs do indeed expand women's representation in CS.