Gender: In the Genes or in the Jeans?

A Case Study on Sexual Differentiation

Part V—“External Genital Differentiation”

by
William J. Hoese, California State University Fullerton
Judith Gibber, Columbia University
Bonnie Wood, University of Maine Presque Isle

Section A

We’ve seen different processes involved in differentiation of the gonads and the ducts. The gonads begin as a single tissue that can differentiate in either the male or female direction, depending on whether or not a Y chromosome is present. But when it comes to differentiation of the ducts, the Y chromosome is not important. Rather, the ducts begin as two sets of tissues, each of which can differentiate in only one direction (either male or female) depending on whether or not testicular endocrine and paracrine signals are present.

What about the external genitals? When we look at these in the early embryo, we see that their development seems to be like the gonads, that is, the male and female genitals are indistinguishable until about four to eight weeks of fetal life, at which time the tissue develops in either a male or female direction.

What regulates differentiation of the external genitals? The chromosomes or the hormones?

Questions

Design an experiment using laboratory rats to distinguish between these two possibilities. What results would you expect if the chromosomes are responsible? What results would you expect if the hormones are responsible?
Fill in the flowchart to reflect differentiation of the genitals.

Go to Part V, Section B—“External Genital Differentiation” (Continued)

Originally published at http://www.sciencecases.org/gender/gender5a.asp