The third stage of psychosexual development proposed by Freud is the phallic stage, occurring between the ages of 3 and 6. During this period, children become aware of their bodies and the differences between males and females. The erogenous zone in this stage is the genitals, and conflicts arise as children develop desires toward the opposite-sex parent. Boys experience the Oedipus complex, where they desire their mother and view their father as a rival. This leads to castration anxiety, the...

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female...

The vulva encompasses the external structures of the female reproductive system. At the forefront is the monpubis, a cushion of fatty tissue atop the pubic bone. Once puberty sets in, this area typically grows hair. Extending from just behind the mons pubis are the labia majora (labia = 'lips'; majora = 'larger'), which are larger skin fs olds coated with hair. Nestled within are the labia minora (labia = 'lips'; minora = 'smaller'), which are thinner, more...

Mate choice—the decision about whom to mate with—is a type of natural selection, since animals must reproduce to pass down their genes. Mate choice is also called intersexual selection because the behavior occurs between the sexes.

The female breast is a hemispheric projection of variable size positioned anterior to the pectoralis major and serratus anterior muscles. A fascia layer composed of dense, irregular connective tissue connects it to these muscles.
Each breast features a pigmented projection known as the nipple, through which milk emerges via closely spaced openings of ducts, referred to as lactiferous ducts. Surrounding the nipple is a circular pigmented area of skin named the areola, which appears rough due to...

Oogenesis,  the process of developing egg cells (female gametes), occurs within the ovaries and is fundamental to female fertility. This sequence begins during fetal development when diploid oogonia in the developing ovaries undergo mitotic divisions to produce primary oocytes. By birth, these primary oocytes enter prophase I of meiosis but become arrested in this stage, remaining suspended until puberty.
Each primary oocyte is surrounded by a layer of pre-granulosa cells, forming what is...