Everyone is born with the potential to be either male or female. Everyone is born with both the Wolffian duct (male duct system) and the Mullerian duct (female duct system). What determines maleness is the the presence of the SRY gene. The SRY gene is what allows testis to develop. Once the testis are developed, the male duct system begins to form.When a male is about to be formed, a hormone called the anti-Mullerian duct hormone is released so that the Mullerian duct system which would develop into a female, would be destroyed. Once the Mullerian duct is destroyed, the formation of the testis, including the epididymus, the vas deferns, seminal vesicle and seminiferous tubules can develop. Within females, they too are born with both the Mullerian and Wolffian duct systems. But what is different within females is that the Wolffian duct system begins to decrease when it realizes that the SRY gene is not there to tell it to develop into testis. Thus the Mullerian duct can now develop into the uterus, the fallopian tubes, cervix and parts of the vagina.
There are two part sex determination stages. One stage determines the sex internally and one stage determines the sex externally. When something goes wrong, you could have internal male sex organs but have external female organs, or vice versa. This is why you could have a person with the outer apperance of a female, but internally their organs are male, and they are not able to produce because they do not have a uterus.
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