The presence of which gene is essential for male phenotype development?

The SRY gene (Sex-determining Region Y) is crucial for male phenotype development because it initiates the process of testis formation during embryonic development. Located on the Y chromosome, SRY encodes a transcription factor that triggers the development of undifferentiated gonads into testes. Once testes form, they produce male hormones, particularly testosterone and anti-Müllerian hormone (AMH), which further direct the male sexual differentiation process and suppress the development of female reproductive structures.

Without the SRY gene, the default sex development pathway occurs, leading to the formation of ovaries and female phenotypic characteristics. The other genes mentioned play important roles in various biological processes but are not directly implicated in the determination of male sex phenotype. Thus, the presence of the SRY gene is essential for triggering the male developmental pathway.