Definition for Testis-determining factor
From Biology Forums Dictionary
Testis-determining factor (TDF) is a protein signal that results in maleness in humans and some other species.
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).
On the converse, such a cross-over event also can result in a Y chromosome that is missing the Sex-Determining Region (SRY), which contains the TDF, replaced with the corresponding sequence from the end of the X chromosome. Individuals that inherit this Y chromosome will develop as females, despite having the normal male chromosomal set of one X and one Y. This is called Swyer syndrome (46XY, genotypic male but phenotypic female).
