Draw a flow chart illustrating the development of bipotential reproductive structures in an XY individual and an XX individual, indicating the stimuli for development or regression of the structures. Add to this chart the changes that occur at puberty and their stimuli. Finally, indicate the points on the chart at which gender anomalies associated with the following conditions occur:

Question

A. testicular feminization or androgen insensitivity (XY genotype, permanent female external morphology
with internal testes and androgen production but faulty androgen receptors);
B. male pseudohermaphrodites (XY genotype and external female morphology with internal testes, and
masculinization occurring at puberty);
C. congenital adrenal hyperplasia (XX genotype with normal female internal organs, masculinized external
organs observed at birth);
D. sexual development is similar in nonhuman mammals, but there are some interesting pathologies not
seen in humans. A freemartin occurs in cattle twins, with one male and one female. The male is normal but
the XX female is sterile, born masculinized, and has testicular tissue. Explain the most likely cause of this
masculinized phenotype, and indicate on your chart the point or points at which something abnormal
occurred.

Answer 1

Chart of normal male development should resemble Figure 26.3 in the chapter, with a similar chart in parallel for
female development. Appearance of secondary sexual characteristics in both genders results from increases in
gonadal steroids.
A.-B. Both testicular feminization and male pseudohermaphroditism begin with lack of response of target tissues
to androgens produced in fetal development; testicular feminization allows development of female secondary
sexual characteristics, whereas pseudohermaphroditism allows masculinization at puberty.
C. Congenital adrenal hyperplasia allows normal development of female internal structures, but masculinizes
external organs before birth as an effect of adrenal androgens. If untreated, puberty-related changes would also be
masculine.
D. The freemartin cow must receive anti-Müllerian hormone through shared placental circulation; therefore
testicular tissue develops and androgens are secreted to produce further masculinization, in the fetus and at
puberty.