Which hormone is primarily responsible for the development of female traits and the regulation of the menstrual cycle?

The hormone primarily responsible for the development of female traits and the regulation of the menstrual cycle is estrogen. Estrogen is crucial for the development of secondary sexual characteristics in females, such as breast development, widening of the hips, and the distribution of body fat.

Additionally, estrogen plays a vital role in the menstrual cycle, particularly in the regulation of the menstrual phases. It helps stimulate the growth of the uterine lining (endometrium) during the follicular phase, preparing the body for a potential pregnancy. If pregnancy does not occur, estrogen, along with other hormones, helps regulate the shedding of this lining during menstruation.

While progesterone also plays an important role in the menstrual cycle, particularly after ovulation when it helps maintain the uterine lining for a possible implantation, estrogen is the key hormone that initiates and regulates the cycle's various stages and is fundamental in establishing female traits.