Final answer:
Mutations ablating androgen receptor function lead to Androgen Insensitivity Syndrome, preventing typical male phenotypic development in XY individuals despite the production of testosterone, resulting in predominantly female characteristics.
Step-by-step explanation:
Mutations that completely ablate the function of the androgen receptor would significantly impact the phenotypic development of humans with XY chromosomes. These individuals are expected to develop a condition known as Androgen Insensitivity Syndrome (AIS), where their bodies cannot respond to androgens like testosterone. Even though testosterone is produced, the lack of receptor function means that masculinization, including the development of male secondary sexual characteristics and the male reproductive system, does not occur as expected. Instead, individuals with this mutation develop predominantly female external genitalia and secondary sexual characteristics, despite having XY chromosomes due to the absence of androgen effects.
Sex differentiation in typical development is initiated by the SRY gene on the Y chromosome, leading to testis development and testosterone secretion. Testosterone normally binds to androgen receptors to facilitate the development of male sexual organs. Without functional androgen receptors, this process is disrupted, resulting in feminized phenotypes in XY individuals. Later in life, during puberty, hormone therapy may be utilized to align physical appearance with gender identity.