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.
Similarly, drugs, chemicals, temperature, and light are among the external environmental factors that can determine which genes are turned on and off, thereby influencing the way an organism develops and functions. Sex-influenced traits are those that are expressed differently in the two sexes.Such traits are autosomal, which means that the genes responsible for their expression are not carried on the sex chromosomes. An example of a sex-influenced trait is male-pattern baldness.imilarly, drugs, chemicals, temperature, and light are among the external environmental factors that can determine which genes are turned on and off, thereby influencing the way an organism develops and functions. Sex-influenced traits are those that are expressed differently in the two sexes.