WHY YOU WERE BORN A FEMALE, AND WHY A MALE DOES NOT HAVE FEMALE GENITALS

 

The reason a female is a female is because she does not have a Y chromosome. In other words, a female is not a female because she has 2X (XX) chromosomes. She is a female because she does not have a Y chromosome. This means, an embryo is pre-destined or programmed to become female and will become female unless something is done to force that embryo to become male, and what forces it to become male has something to do with the Y chromosome. If there isn’t a Y chromosome, then the  embryo will become a female as the embryo was pre-programmed to be. This leads to the question; what is it about the Y chromosome that accomplishes this?

There is a region on the Y chromosome called the SRY segment. SRY means Sex determining Region of the Y chromosome. The SRY segment codes for the Testis Determining Factor (TDF). And so the Y chromosome has TDF. The TDF will cause the gonad to become a Testis. In the abscense of TDF, in other words if there’s no Y chromosome, then that gonad will become an ovary as it was pre-programmed to do. So whether or not there is TDF, determines whether there will be a testis or an ovary. Ones a testis is formed, the endocrine cells of the testis for example the LEYDIG cells of the testis secrete testosterone. The presence of testosterone as well as a derivative of testosterone called dihydrotestosterone causes all the remainder of the male genital system to develop including the vas deferens, the penis, the prostate, the scrotum, the seminal vesicle, epididymis etc.

An embryo is pre-programmed to become a female, which means the embryo is pre-programmed to develop a female genital system. In other words, the embryo is pre-programmed to have a uterus, fallopian tube, vagina etc. And so if you want this embryo to be normal male, not only do you have to form the male genital system, but you also have to prevent the formation  of the female genital system. This is accomplished with a substance called Mullerian Inhibiting Factor (MIF). Mullerian refers to the Mullerian ducts also known as paramesonephric ducts which are the embryonic ducts that give rise to the female genital tract ( the fallopian tubes, the uterus, cervix etc). And so if you inhibit the development of the Mullerian ducts, you inhibit the formation of the female genital tract. MIF comes from the Sertoli cells (another cell type found in the testes). Therefore the testes give the testosterone and also provide the MIF which will inhibit the formation of the female genital tract. And so with all the factors(TDF,testosterone and MIF) acting together, you end up with testes and a normal male genital system,  and without a female genital system. But if there is no Y chromosome, there’s no TDF. If there’s no TDF, instead of TESTES, you will have ovaries. With an ovary, you don’t have have high level of testosterone, and so you will not develop the male genital system and you will not be able to inhibit the Mullerian ducts  and so you develop the female genital system.

If you think through the possible abnormalities, you can see how you could end up with an embryo that have mixed gender abnormalities. For example, if you have an embryo that has a Y chromosome and therefore has TDF, testes and secretes testosterone, but lets say for whatever, that embryo isn’t producing MIF or isn’t producing the receptors for MIF. In this case, that embryo will have testes,a male genital tract, but will also have a female genital tract. This will be one version of a mixed gender abnormality.