The upper part of the trapezius muscle is the primary target of the shoulder shrug. The trapezius is a triangular muscle that makes up the upper back, running from the back of the neck and down along the spine, lying over the shoulder blades.
In general terms, sex refers to the biological differences between males and females, such as the genitalia and genetic differences. Gender is more difficult to define but can refer to the role of a male or female in society (gender role), or an individual's concept of themselves (gender identity).
The population of the world is divided between males and females though there are also people who have an intersex gender. Thus, it becomes clear that gender is defined by our sex organs and our mind or sexual orientation has nothing to do with our gender.