The platysma is a superficial muscle that overlaps the sternocleidomastoid. It is a broad sheet arising from the fascia covering the upper parts of the pectoralis major and deltoid; its fibers cross the clavicle, and proceed obliquely upward and medially along the side of the neck.
For example genetic differences, females inherit X chromosomes from their father giving them a genetic make-up of XX, while males inherit a Y chromosome from their father, thus giving them a genetic make-up of XY.
Their study shows male to female transsexuals are more likely than non-transsexual males to have a longer version of a receptor gene for the sex hormone androgen or testosterone. The findings from the largest-yet genetic study of male to female transsexualism are published online today in Biological Psychiatry.