In this picture, a woman with an X-linked dominant disorder has a 50% chance of having an affected daughter or son with each pregnancy.
The reason for hypertrichosis occurring is because there is an extra chunk of genes in the X-chromosome. The extra DNA may switch on a hair-growth gene nearby, resulting in runaway furriness.
"The best bet for a culprit, wrote study researcher Pragna Patel of the University of Southern California, is a gene called SOX3, which is known to play a role in hair growth."