Thus far we have considered only typical prenatal differentiation. However, much of what is known about the impact of biological sex differentiation on the development of gender identities comes from studies of atypical differentiation. We have seen that the differentiation of internal and external sex structures occurs under the influence of biological cues. When these […]

Important structural and functional differences in the brains of human females and males are in part a result of prenatal sex — differentiation processes (Becker et al., 2008; Hines, 2004; McCar­thy et al., 2011). Many areas of the developing prenatal brain are significantly affected by circulating hormones (both testosterone and estrogen), which contribute to the […]

The external genitals develop according to a similar pattern. Until the gonads begin releasing hormones during the 6th week, the external genital tissues of male and female fetuses are undifferentiated (I Figure 5.3). These tissues will develop into either male or female external genitals, depending on the presence or absence of a testosterone product known […]

By about 8 weeks after conception the sex hormones begin to play an important role in sex differentiation. The two duct systems shown in Figure 5.2a—the Wolffian ducts and the Mullerian ducts—begin to differentiate into those internal structures shown in Figure 5.2b. In a male fetus, androgens secreted by the testes stimulate the Wolffian ducts […]

The gonads produce hormones and secrete them directly into the bloodstream. Ova­ries produce two classes of hormones: estrogens (ES-troh-jens) and progestational compounds. Estrogens, the most important of which is estradiol, influence the devel­opment of female physical sex characteristics and help regulate the menstrual cycle. Of the progestational compounds, only progesterone is known to be physiologically […]

In the first weeks after conception the structures that will become the reproductive organs, or gonads, are the same in males and females (see 1 Figure 5.2a). Differentiation begins about 6 weeks after conception. Genetic signals determine whether the mass of undifferentiated sexual tissue develops into male or female gonads (Dragowski et al., 2011; Wilhelm […]

Our biological sex is determined at conception by the chromosomal makeup of the sperm (male reproductive cell) that fertilizes an ovum, or egg (female reproductive cell). Except for the reproductive cells, human body cells contain 46 chromosomes, arranged in 23 pairs (see 1 Figure 5.1). Twenty-two of these pairs are matched; that is, the two […]

Typical Prenatal Differentiation From the moment of conception many biological factors contribute to the differentia­tion of male or female sex. In the following paragraphs, we explore how biological sex differentiation occurs during prenatal development. Our discussion follows a chrono­logical sequence. We begin at conception, looking at chromosomal differences between male and female, and then continue […]

At a Glance ■ TABLE 5.1 Gender Identity as a Biological Process-Typical Prenatal Differentiation Characteristic Female Male Chromosomal sex XX XY Gonadal sex Ovaries Testes Hormonal sex Estrogens progestational compounds Androgens Internal Fallopian tubes Vas deferens reproductive structures Uterus Inner portions of vagina Seminal vesicles Ejaculatory ducts External genitals Clitoris Inner vaginal lips Outer vaginal […]

Gender identity refers to each individual’s personal, subjective sense of being male or female. Most of us realize in the first few years of life that we are either male or female. However, there is no guarantee that a person’s gender identity will be consistent with his or her biological sex, and some people experience […]