| Development of sexual organs |
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| Dear Dr. Massoud: I read that at fetal age we all were bisexuals. Is that true? How come that our genitals differentiate later on into a very distinguished male and female organs? |
The determination of our sexual identity starts at the moment of conception: If a sperm cell carrying one X chromosome fertilizes the mother’s ovule (eventually carrying one X chromosome only) then the fetus will be a female, however if the fertilizing sperm cell carries one Y chromosome then the fetus is a male. This phase is called the genetic determinism.
During the first 8 weeks of conception, fetuses look physically females even though they might males and do have the same primitive sexual organs. This is what is meant by “at fetal age we are all bisexuals”.
After week 8 for males and week 12 for females, these primitive organs start to gradually differentiate into male or female genitalia thanks to specific maternal sexual hormones and the hormones produced by the SRY gene found on chromosome Y (in case of a male). The figure below shows that even after week 12, the genitals are still difficult to be distinguished from each other.
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As the fetus keeps on developing, the genitals and the annex organs start to become more visible.
- In the case of a female between weeks 9 and 12, the anus starts to appear 9, and so do the glans clitoridis (that will give the clitoris) and the urethral groove. By the end of week 12, the vestibule of the vagina and the pre-hymen are formed. Later on, the ovaries will be located inside the female’s body, and the vagina will be totally separated from the urethra.
- In the case of a male, the clitoris is substituted by the penis, and the ovaries by the testicles that locate outside the body. Contrary to females, the urethra will be a common duct used for urination and sperm ejaculation in males.
The figures below show a comparison between the development of male and female genitalia and how these latter look like from birth till term. |
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