Everything about Testis Determining Factor totally explained
Testis-determining factor (
TDF) is a general term for the
gene (or product thereof) that results in
maleness in humans and some other species.
Certain genes cause chemical reactions that result in the development of
testes.
Embryos are
gonadally identical, regardless of genetic sex, until a certain point in development; then the testis-determining factor causes male
sex organs to develop, while lack of this factor will cause the embryo to develop as physically
female.
The TDF factor is encoded by the
SRY gene located in the
Y chromosome. It is a
DNA binding protein, that enhances other
transmission factors, or is a transcription factor itself. Its
expression directly or indirectly causes the development of primary
sex cords, which will later develop to
seminiferous tubules. These cords form in the central part of the undifferentiated-yet
gonad, turning it into a
testis. The testis then starts secreting
testosterone and the
Mullerian Inhibiting Substance.
Older texts discuss the role of the
HY antigen in the control of testicular development, but this was later disproven.
Role in disease
The TDF gene has some interesting implications. The
genetic recombination of
Crossing over can cause the gene to be transferred on to the X chromosome. In this case, the X chromosome will initiate
testis development, so regardless of whether the person has a Y chromosome, the person will turn into a male. Though everything else will be developed as if it were a female (other sex related
alleles), the apparent sex will be male (a syndrome known as
XX male syndrome).
Conversely, such a cross-over event also can result in a Y chromosome that's missing its TDF, replaced with the corresponding sequence from the end of the X chromosome. Individuals who inherit this Y chromosome will develop as females, despite having the normal male chromosomal set of one X and one Y. However, the lack of two X-chromosomes gives complications to such females, called
Turner syndrome.
Further Information
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