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Chapter 11 Reproductive Behaviors

Chapter 11 Reproductive Behaviors. Variations in Sexual Behavior. Gender identity : how we identify sexually and what we call ourselves Sex differences : Biological differences between males and females

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Chapter 11 Reproductive Behaviors

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  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. Most people have a gender identity that matches their external appearance. Some people have a gender identity that is opposite their biological sex. Gender Identity

  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. Variations in Sexual Development • True hermaphrodite: someone who has both testicular and ovarian tissue—very 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)

  6. Video: Is It a Boy or a Girl?

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

  8. Sex Hormones Two types of sex hormones include: • Androgens • Estrogens • Both sexes have both hormones

  9. 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

  10. 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. Sex and Hormones

  11. 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).

  12. 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.

  13. 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.

  14. 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.

  15. XX female’s 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. Congenital adrenal hyperplasia (CAH)

  16. 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. Congenital adrenal hyperplasia (CAH)

  17. 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 cell’s 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) Androgen insensitivity or testicular feminization

  18. 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.

  19. 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.

  20. 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. Biological Bases of Sexual Orientation

  21. 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. Biological Bases of Sexual Orientation

  22. 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. Biological Bases of Sexual Orientation

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

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