Y Chromosome & Male Development
Normal male mammals have a single X chromosome and thus have no Barr Bodies. However, we know from Turner Syndrome (XO) females that the presence of a single X alone will not cause a mammal to be male. Research has shown that a gene on the Y chromosome, called SRY (for sex- determining region Y), is important for male development in mammals. The SRY protein appears to bind to DNA, distorting its normal helical structure. This distortion may allow other genes to be expressed, ultimately leading to testes formation. The testes then produce testosterone, which is critical for the development of male secondary sex characteristics.