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.
At birth, babies are assigned male or female based on physical characteristics. This refers to the sex of the child. Most children's gender identity aligns with their biological sex. However, for some children, the match between biological sex and gender identity is not so clear.