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Modern Genetic Analysis Chapter 16. The Genetic Basis of Development Binary Fate Decisions: Pathways of Sex Determination
Table 16-1. A Comparison of the Features of Sex Determination in Drosophila and Mammals

Aspect of sex determination | Drosophila | Mammals

Chromosomal basis of XX versus XY | X:A ratio | Presence or absence of Y
Molecular basis of XX versus XY | Numerator:denominator transcription factor subunit interactions | Transcription factor for testis determination located on Y chromosome
Decision-making process organ instructing other tissues | Cell by cell | Testis acts as source of male-determining organ instructing other tissues
Switch | Transcription of Sxl (Sex lethal) in early embryo | Presence or absence of SRY (human) ~ Sry (mouse) gene
Level of downstream regulation | Alternative mRNA splicing | Transcription
Positive feedback mechanism development | Positive feedback loop of SXL protein on Sxl mRNA splicing | Continued presence of testis throughout
Elaboration of sex-specific gene expression | Presence of male- or female-specific form of dsx (doublesex)-encoded protein. Generally, DSX-F is a represssor of expression of male-specific genes, and DSX-M is a represssor of female-specific genes. For a few genes, DSX-F or DSX-M may act as activators of female-specific or male-specific gene expression. | Testosterone-mediated activation of androgen receptor in target tissues. Testosterone-androgen receptor regulates transcription by binding to testosterone-responsive elements (enhancers and silencers).

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