Abstract: Normal sex differentiation includes the formation of primordial gonads, sex determination and ovarian or testis development. The misregulation of gene expression in each process may lead to the disorders of sex development（DSD）. DSD is defined by congenital conditions of the atypical chromosome，gonadal or anatomical sex. With the development of molecular biotechnology，more and more genes and signaling pathways are discovered to be involved in sex differentiation and development. For example，some genes such as SRY、SF1、WT1 and Sox9 are closely related to testicular development, while others such as Wnt/Rspo1/B-catenin pathway and genes like Dax1、Foxl2 play an important role in ovarian differentiation. Some none-coding RNA and transforming growth factor also regulate the sexual differentiation. The developments of both testis and ovary are active, and transverse differentiation can appear according to some abnormal genes even after birth.

Key words: Testis, Ovary, Gonadal dysgenesis, Y chromosome, Sex determination (analysis), MicroRNAs, Signal transduction