Hormones, Brain, and Behavior:
Putative Biological Contributions
to Cognitive Sex Differences
Roslyn Holly Fitch
Heather A. Bimonte
Anyone who has attended a 17-week ultrasound in a healthy pregnancy is fainiliar with the query, [Do you want to know the sex?] If the answer is yes, a simple visual inspection of the fetal profile (if baby cooperates) is typically sufficient to satisfy curiosity. However, a more reliable indication of fetal sex is provided through amniocentesis, in which the chromosomal profile of the fetus is assessed (in most cases, for reasons other than sex determination). Although expectant parents waiting to pick nursery room colors know that ultrasound sex-determination may or may not be reliable, amniocentesis is almost definite. The reason is that chromosomes determine gonadal sex and, in all but a few developmentally anomalous conditions, gonadal sex determines phenotypic sex.
In early fetal mammalian development, the gonadal system is equipotential or [indifferent.] At this developinental time point, the sexual characteristics of the fetus are not yet established. However, a genetically normal fetus will carry either an XX or XY sex chroinosome pair. It is the presence or absence of the Y chromosome (and more specifically, a gene on the Y chroinosome) that will determine