Lecture PowerPoint Presentation for Chapter 4

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4
Sex and Gender
Differences
Genes and Hormones Guide Sex Development
Testes and ovaries form from the precursor gonads
The gene that instructs the ridges to differentiate into testes
is called SRY
This gene is located on the Y chromosome
Figure 4.1 Human chromosomes
Male and Female Reproductive Tracts Develop from Different
Precursors
Embryos of both sexes possess both Wolffian and
Müllerian ducts
• Wolffian ducts are precursors of the male reproductive
tract
• Müllerian ducts are precursors of the female
reproductive tract
In males, testes produce anti-Müllerian hormone (AMH) to
eliminate the female ducts
In females, the absence of AMH allows Müllerian ducts to
persist and to develop into the oviducts, uterus, and deeper
parts of the vagina
Figure 4.2 Development of the male and female reproductive tracts
Male and Female External Genitalia Develop from the Same
Precursors
Female and male external genitalia have the same
developmental origin
Most prenatal sex development occurs during weeks 8
through 24 of gestation, when testosterone levels are high
in male fetuses
The testicles descend during development
Figure 4.3 Development of the male and female external genitalia (Part 1)
Figure 4.3 Development of the male and female external genitalia (Part 2)
Figure 4.3 Development of the male and female external genitalia (Part 3)
Figure 4.4 Descent of the testicles (Part 1)
Figure 4.4 Descent of the testicles (Part 2)
The Brain Also Differentiates Sexually
There are differences in brain structure, function, and
chemistry between the two sexes
• These differences are brought about by higher levels of
androgens in males than in females during
development
Sex Development May Go Awry
Chromosomal anomalies that do not fall under typical
female (46,XX) or male (46,XY) chromosomal
complements affect growth and fertility
• Klinefelter syndrome (XXY, XXXY)
• Turner syndrome (XO)
• XYY syndrome
• Triple-X syndrome
The gonads or genitals may be sexually ambiguous
• Gonadal intersexuality
• Congenital adrenal hyperplasia (CAH)
• Androgen Insensitivity Syndrome (AIS)
Figure 4.6 Partial masculinization of genitalia in a girl with congenital adrenal hyperplasia
Box 4.1 Personal Points of View: My Life With Androgen Insensitivity Syndrome
Gender Is a Central Aspect of Personhood
Gender identity is the sense of which sex one belongs to.
For some people, gender identity does not match
anatomical sex
This identity is expressed via gender role behavior
Sexual orientation, cognition, and personality traits differ
between men and women
Differences in sexuality include attitudes toward casual sex,
jealousy, and frequency of masturbation
Figure 4.7 Mental rotation task
Figure 4.8A Test of object location memory
Figure 4.8B Test of object location memory
Gender Is a Central Aspect of Personhood
Many gender differences arise at a young age
• By about 3 years of age, most children show evidence
of gender constancy
• By about 1 year of age, most children can distinguish
between men and women
• Differences in toy preferences
Figure 4.9 Gender constancy
Figure 4.10 Toy preference test
Biological Factors Influence Gender
Evolutionary factors influence gender development
• Evolutionary factors:

Cognitive differences between the sexes due to
long-standing division of labor between men and
women

Difference in interest in casual sex between men
and women

Jealousy
Figure 4.11 Monkeys show humanlike toy preferences
Experiments Demonstrate a Role for Sex Hormones
Girls with CAH have behavioral traits shifted in the
masculine direction
Prenatal androgens influence gender
The 2D:4D ratio correlates with many gendered
characteristics
Box 4.2 Biology of Sex: “Eggs at Twelve”
Box 4.3 Personal Points of View: The Boy Who Was Raised as a Girl
Figure 4.12 Hormones and play
Figure 4.13 Finger-length ratio and gender
Life Experiences Influence Gender
Life experiences influence gender development beginning
early in life
• Observing socialization
• Rewards and punishments
• Imitation
Cognitive models focus on thought processes
• Gender schemas
• Sexual scripts
Figure 4.14 Babies enter a gendered world
Figure 4.15 Influence of siblings on gender
Figure 4.16 The media influence gender
Figure 4.17 Influence of gender stereotypes on children’s memories
Transgendered People Cross Society’s Deepest Divide
Unhappiness caused by discordance between anatomical
sex and gender identity is called gender dysphoria
• F-to-M transexuals (trans men)
• M-to-F transexuals (trans women)

Transvestism

Autogynephilia
Transgendered People Cross Society’s Deepest Divide
• Sex-reassignment is a multistage process
• Some transexuals do not desire surgery
• Some medical centers treat pre-pubertal children
affected by gender dysphoria
• Transgenders and transexuals struggle for awareness
and acceptance
Figure 4.19 Chastity Bono transitioned to Chaz Bono in 2009
Figure 4.20 The vulva after sex-reassignment surgery
Figure 4.21 Transformation of the clitoris into a small penis
Box 4.5 Controversies: How Should We Treat Gender-Dysphoric Children?
Figure 4.22 Kate Bornstein

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