Sex expression is strongly, but not perfectly, correlated with the existence or absence of the Y chromosome. Genetically, and biologically, sex determination ca

Sex expression is strongly, but not perfectly, correlated with the existence or absence of the Y chromosome. Genetically, and biologically, sex determination can be complicated by, at least: nonfunctional Y, XXY, XYY, and other issues. In these cases, (about 1% of the general population), sex is not determined biologically according to the binary standard. This doesn’t even take into account social sex determination, or gender identification, which are psychological (and physiological!) in scope & involve a much more complicated biological system.