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Chapter 11 Reproductive Behaviors

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Sexual Differentiation. The male Y chromosome includes the SRY gene which causes the primitive gonads to develop into testes, the sperm-producing organ. – PowerPoint PPT presentation

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Title: Chapter 11 Reproductive Behaviors


1
Chapter 11Reproductive Behaviors
2
Variations in Sexual Behavior
  • Gender identity how we identify sexually and
    what we call ourselves
  • Sex differences Biological differences between
    males and females
  • Gender role refers to the activities and
    dispositions that a particular society encourages
    for one sex or the other

3
Gender Identity
  • Most people have a gender identity that matches
    their external appearance.
  • Some people have a gender identity that is
    opposite their biological sex.
  • Jazz is a transgender child. See her story at
  • Link to Video
  • (Extra credit opportunity)

4
  • Psychologists and researchers once believed that
    gender identity was learned and more a product of
    rearing and experience.
  • Current evidence strongly suggests that
    biological factors, especially prenatal hormones,
    play a large role in gender identity.

5
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6
Variations in Sexual Development
  • True hermaphrodite someone who has both
    testicular and ovarian tissuevery rare
  • Hermaphrodites individuals whose genitals do not
    match the normal development for their genetic
    sex
  • Intersex people are people are intermediate
    between being male or female (AKA
    pseudohermaphrodite)

7
  • Video Is It a Boy or a Girl? (1999)
  • Link to Video, Part One
  • Link to Video, Part Two
  • Link to Video, Part Three

8
Sex Hormone Endocrine glands
  • A chemical that is secreted by a gland, conveyed
    by the blood, and affects other organs
  • Glands that produce hormones

9
Sex Hormones
  • Two types of sex hormones include
  • Androgens
  • Estrogens
  • Both sexes have both hormones

10
Sex and Hormones
  • Androgens are a groups of male sex hormones that
    include testosterone
  • Generally referred to as male hormones because
    men have higher levels than women

11
Sex and Hormones
  • Estrogens include estradiol and others and are
    referred to as female hormones because women
    have higher levels.
  • Progesterone is a type of hormone that prepares
    the uterus for the implantation of a fertilized
    ovum and promotes the maintenance of pregnancy.

12
Sexual Differentiation
  • Begins with the chromosomes
  • At six weeks of development, both sexes have
    primitive gonads as well as
  • Mullerian ducts (precursors to female
    reproductive organs-- oviducts, uterus, and upper
    vagina) and
  • Wolffian ducts (precursors to male reproductive
    organs--vas deferens and seminal vesicles).

13
Sexual Differentiation
  • The male Y chromosome includes the SRY gene which
    causes the primitive gonads to develop into
    testes, the sperm-producing organ.
  • The developed testes produce the hormone
    testosterone.
  • Testosterone induces the development of the penis
    and scrotum.
  • Females are not exposed to high testosterone
    levels and their gonads develop into ovaries, the
    egg-producing organs.

14
Sex and Hormones
  • Sensitive periods are early periods when hormones
    have long-lasting effects.
  • Sexual differentiation depends mostly on the
    level of testosterone during a sensitive period.
  • The human sensitive period for genital formation
    is about the third and fourth month of pregnancy.

15
Sex and Hormones
  • Sex hormones can have the following effects
  • Organizing effects- occur mostly at sensitive
    stages of development.
  • -Determine whether the brain and body will
    develop male or female characteristics
  • Activating effects- occur at any time of life and
    temporarily activate a particular response.

16
Congenital adrenal hyperplasia (CAH)
  • XX females cortisol production leads to
    overstimulation of the adrenal gland.
  • Overstimulation of the adrenal gland leads to
    extra testosterone production.
  • The female fetus becomes partly masculinized.

17
Congenital adrenal hyperplasia (CAH)
  • Research indicates that CAH girls show a greater
    preference for boy-typical toys than do other
    girls.
  • During adolescence and early adulthood, they also
    show partly masculinized interests.
  • Sexual interest and activity also differs for CAH
    girls as well.

18
Androgen insensitivity or testicular feminization
  • XY male has the genital appearance of a female.
  • Production of androgens remains normal but they
    lack the androgen receptor that enables it to
    activate genes in a cells nucleus.
  • Condition occurs in various degrees from a
    smaller than average penis to genitals that
    develop a female appearance.
  • Four siblings with testicular feminization
    syndrome (recessive sex-linked allele)

19
5 alpha-reductase 2 deficiency
  • XY males fail to produce an enzyme that converts
    testosterone to dihydrotestosterone.
  • Most look female at birth but a penis develops
    during adolescence and puberty.
  • Most then accept a male gender identity.
  • Brain is exposed to testosterone during early
    development.

20
Biological Bases of Sexual Orientation
  • Research suggests that certain brain structures
    differ in size between heterosexual and
    homosexual men and women, due to the early role
    of sex hormones.
  • Sexually dimorphic nucleus (SDN) an area in the
    anterior hypothalamus that is larger in the male
    and contributes to control of male sexual
    behavior, (e.g., being attracted to a female).
  • Study of homosexual male brains found that their
    SDN was similar to those found in females.

21
Biological Bases of Sexual Orientation
  • Twin studies suggest genetic factors.
  • Probability is highest in monozygotic twins and
    lower in dizygotic twins, and even lower in
    siblings and adopted brothers or sisters.
  • Because monozygotic twins can have opposite
    sexual orientations, genes are not the only
    factor.

22
Biological Bases of Sexual Orientation
  • Sexual orientation may be influenced by
    testosterone levels during sensitive periods of
    brain development.
  • Male animals deprived of testosterone early in
    life show sexual interest in other males as
    adults.
  • Female animals exposed to testosterone during
    early development show an increased likelihood of
    mounting behavior.

23
Biological Bases of Sexual Orientation
  • Laboratory research has also shown that prenatal
    stress can alter sexual development.
  • Male subjects subjected to either prenatal stress
    or alcohol developed male sexual behavior in
    addition to female sexual behaviors.
  • Male subjects exposed to both stress and alcohol
    during prenatal development had decreased sexual
    behavior.

24
Biological Bases of Sexual Orientation
  • The probability of homosexual orientation is
    higher among men with older brothers.
  • Results suggest that a mothers immune system may
    react against a protein in a son and attacks
    subsequent sons to alter development. Prenatal
    Influences, p337
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