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10-1 Sexual Development ● ●

Sex refers to biological sex Gender is usually applied in situations that involve social, learned and personal aspects

10-1a The Genetics of Sex ●

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An individual’s genetic sex begins with sex chromosomes inherited from two parents ○ Mothers provide an X chromosome to all of their offspring ○ Fathers provide either a X chromosome or a Y chromosome to produce either a female or a male The initial receipt of an XX or XY genotype begins a cascade of hormonal, structural and behavioral events Karyotype: a profile of chromosome number and appearance in the nucleus of a cell as seen under a light microscope Sex chromosomal abnormalities occur in about 1 out of every 426 children ○ Having a mosaic karyotype means that a single individual has cells with differing complements of chromosomes Down Syndrome: an individual has three full or partial copies of the 21st chromosome Abnormalities due to a third sex chromosome appear to have relatively mild effects ○ Out of the possible combinations of three sex chromosomes, females with an XXX genotype experiences t ○ Significant abnormalities typically arise in cases involving more than three sex chromosomes Turner syndrome ○ Turner syndrome: a condition caused by an XO (a single X chromosome) genotype, characterized by freq and infertility ○ Some studies have shown that cases where the maternal X is passed to daughters outnumber cases in wh along by a factor of 3:1 ○ Usually infertile due to abnormally developing ovaries ■ Ovaries can develop abnormally into “streak gonad” ○ Associated with short stature, skin folds in the neck, and difficulty with spatial relations tasks ○ Many show chromosomal mosaicism ■ Frequently features cryptic mosaicism ○ Intelligence is normal ○ Human growth hormone, plastic surgery, female hormone replacement therapy and assisted reproductive t Klinefelter Syndrome ○ Klinefelter Syndrome: a condition in males caused by an XXY genotype, characterized by frequent probl characteristics and verbal skills ○ The most common genetic abnormality related to the sex chromosomes ○ Individuals are phenotypically male, but usually experience reduced fertility and require hormone treatmen development of secondary male sex characterstics (facial hair, deeper voice, development of external geni characterists such as breast development ○ Associated with normal intelligence that may be marked by mild cognitive difficulties and social awkwardne ■ Cognitive difficulties usually take the form of delayed and reduced verbal skills ○ Left-handedness is more common ■ Suggests that Klinefelter might affect brain lateralization or the localization of specific functions suc or the other 47, XYY syndrome ○ Also referred to as Jacob syndrome ○ Occurs in 1 of every 1,000 male births ○ Boys appear to be physically within typical limits ■ Tend to be somewhat taller and leaner, suffer from acne and have a higher risk for minor physical a chest ○ Average IQ scores are slightly below the average ○ Language difficulties and autism spectrum disorder are common ○ Men are fertile, but they are slightly more likely than typical men to produce sperm with sex chromosome a ○ Men show a significantly higher rate of antisocial and criminal behavior Lessons learned from individuals with sex chromosome abnormalities

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Each gene produces a protein ■ We can see dose-dependent effects of a genotype on the resulting nervous system A number of genes on the X chromosome escape X-inactivation Regions on the X chromosome that are under-expressed are correlated with visuospatial deficits O i i l t d ith b l d fi it

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absence of anti-Mullerian hormone ○ Testosterone: an androgen produced primarily in the testes ○ Anti-Mullerian hormone: a hormone secreted by fetal testes that causes the degeneration of the Mulleria ○ Androgen: a steroid hormone that develops and maintains typically masculine characteristics ○ In the absence of any androgens or anti-Mullerian hormone, the Mullerian system will develop in the typica ○ In the absence of androgens, the Wolffian system regresses ○ Androgen insensitivity syndrome (AIS): a condition in which a genetic male fetus lacks functional andro development of female external genitalia and typically female gender identity and sexual behavior ■ Fetuses with AIS have an XY genotype and normal testes that remain undescended within the abdo ■ Anti-mullerian hormone still works normally, so the female Mullerian system also fails to develop ● The result is a shallow vagina and no ovaries, fallopian tubes, or uterus ■ Adult individuals with AIS are infertile, but their external appearance is typically female ○ Gender identity: the sense of being male or female, independent of genetic sex or physical appearance ○ Individuals with AIS are genetic males but typically have female appearance and female gender identities ■ Many marry and engage in typical female sexual behavior ○ Incomplete forms of AIS might be an advantage for women in sports due to the effects of androgens on mu carrying capacity capacity of the blood ■ Most international sports organizations have now eliminated genetic testing Development of the external genitalia ○ Follows the differentiation of the gonads during the 6th gestational week ○ The male external genitalia include the penis scrotum ○ The female external genitalia include the labia, clotoris and outer part of the vagina ○ Healthcare providers typically use the Prader scale to assess the relative masculinization of the external ge

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No hormonal activity is required to develop female external genitalia ■ Hormonal stimulation is essential for the development of male external genitalia 5-alpha-dihydrotestosterone: an androgen secreted by the testes that masculinizes the external genitalia ■ Must be recognized by receptor sites for the male external genitalia to develop normally If genetic females are exposed prenatally to excess androgens, their genitalia become masculinized Congenital adrenal hyperplasia (CAH): a condition in which a fetus is exposed to higher-than-normal an masculinization of external genitalia and some cognitive behaviors in affected females ■ Males with CAH show few observable effects related to dexual development, because male fetuses high levels of circulating androgens ■ In females, the clitoris is enlarged, the labia look similar to a scrotum, and in some cases, there is n ● Females with CAH more frequently describe themselves as tomboys, engage in more male than other women to engage in bisexual and lesbian behavior ● BUT the majority of bisexual and lesbian women are heterosexual

10-1c Development at Mini-puberty ● ● ● ●

Males experience a second surge of androgen exposure between the ages of 1-3 months, diminishing by about th This period is called mini-puberty The most obvious outcome of this exposure is an increase in the length of the baby’s penis Prenatal exposure to androgens has been linked to a number of behaviors, including toy choice and aggressivene

10-1d Development at Puberty

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Secondary sex characteristics: characteristics related to sex that appear at puberty, including deepening voice a and widening hips and breast development in females T i l t b t

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The aries produce small amounts of androgens, including testosterone In males, the burst of additional androgens stimulates muscular development, maturity of the external geni of the larynx ■ Testosterone begins to regulate the production of sperm ■ Testosterone also affects a male’s hairline and can result in baldness later in adulthood ○ In females, estradiol produces breast growth, maturity of the external genitalia, maturity of the uterus and c fat distribution and quantity ■ LH and FSH regulate the menstrual cycle ○ In both sexes, estradiol slows down skeletal growth 5-alpha-reductase deficiency: a rare condition in which a child is born with ambiguous genitalia but develops ma secondary sex characteristics at puberty

10-2 Sex Differences in Hormones, Brain Structure and Behavior ●

Continued expression of genes on both X and Y chromosomes continue to push the individual in one of many poss directions ○ Especially in the brain, hormone effects and epigenetics

10-2a The Organizing Role of Sex Hormones ● ● ● ● ● ●

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Sex hormones are classified as steroids Adult females produce about 10% of the amount of androgens produced by adult males Sex hormones play both organizational and activating roles in development Organization: the permanent effects of sex hormones on body structures Activation: reversible effects of sex hormones on body structures and functions Organization during development ○ Between gestational weeks 6-24, mini-puberty and finally at puberty ○ For males, their testosterone levels are particularly high ○ Estradiol influences apoptosis in both sexes ○ Certain parts of the brain are sexually dimorphic ■ Sexually dimorphic: structurally different in males and females ■ Gray matter volume in cortical areas known to be sexually dimorphic Markers of prenatal hormone environments ○ One possible biomarker for the prenatal hormonal environment is the relative length of the digits of the han ■ Specifically the relationship between the length of the index finger and the ring finger ■ 2D:4D ratio ● Males’ ratios are typically smaller than female ratios ● Girls with lower 2D:4D ratios are more likely to be labeled as tomboys

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Another potential marker for prenatal hormonal exposure occurs in the inner ear ■ Otoacoustic emissions: sounds emitted by the cochlea of the inner ear that show sex differences ■ Females produce louder and more frequent otoacoustic emissions

10-2c Sexual Dimorphism in the Brain ● Masculinizing a brain or nervous system ○ Identify features that are sexually dimorphic ■ Display structural differences between the sexes ○ Masculinizing the brain would result in the male pattern in any sexually dimorphic feature ● Sexually dimorphic nucleus of the preoptic area (SDN-POA): a nucleus in the preoptic area of the hypothalam in female rats ○ Development reflects the early organizing effects of hormone exposure ○ Humans: most organizing effects occur prenatally ○ Rats ■ Critical window exists within a few days of birth in which exposure to androgens masculinizes the b ■ At birth, the SDN-POA of rats is approximately the same size in males and females ■ The SDN-POA of the male begins to grow rapidly during the newborn period ■ If a newborn female rat is injected with testosterone, its SDN-POA will be much larger than normal ● Interstitial nuclei of anterior hypothalamus (INAH-1): A collection of four small nuclei in the anterior hypotha INAH-3) appear to be sexually dimorphic. ○ The size of INAH-3 might be associated with male sexual orientation ● Spinal nucleus of the bulbocavernosus (SNB): Motor neurons in the spinal cord that innervate the male the penis ○ These muscles are missing in adult female rats ○ Males and females both possess these muscles and about the same number of SNB cells ○ During the critical period, the low levels of androgens in female rats cause the muscles and most of ● Sex differences in rates of neurogenesis and apoptosis account for findings of different volumes in particula ○ Differences in structures such as SDN-POA that are involved with reproduction appear more likely to death, while differences in structures such as the hippocampus and amygdala are more likely to resu neurogenesis

10-2d Sex Differences in Behavior and Cognition ●

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Play behavior ○ Parents act as key socializing agents early in childhood ○ Androgen exposure as measured in maternal blood or amniotic fluid is predictive of masculine toy interest ○ Children begin to prefer sex-typed toys between the ages of 12 and 18 ■ Children are unable to match sex-typed toys with male or female faces or voices Gender identity: person’s self concept as male or female and is usually viewed as the end product of years of soc ○ Transsexuality: have a gender identity that is inconsistent with biological sex ■ Rare in biological females (.005%) ■ Approximately 3% of women with CAH, raised as girls, express a wish to live as men ■ Might occur due to prenatal timing of hormone influences on the reproductive system and on the br ■ BSTc and INAH-3 conformed to male patterns ■ BSTc does not show sexual dimorphism before puberty, while many transexual individuals express younger ages ○ Examinations of brain structure volume in adolescents with gender dysphoria ■ Individuals who experience distress due to their sex an dgender ■ GD youth are much more similar to those sharing their birth sex than with others sharing their prefe Personality ○ Higher empathy in females ○ Higher physical aggression in males ○ Females with CAH showed decreased empathy and increased physical aggression ■ Boys and girls with high amniotic fluid levels of testosterone or prenatal exposure to androgen med Cognition ○ Males have a slight advantage in visuospatial tasks ■ Early in life ■ Correlated with current testosterone levels ○ Females have a slight advantage in verbal tasks and episodic memory ■ Correlated with higher levels of estrogen ■ Men who received testosterone supplements improved their scores on verbal fluency tests by 20% ○ CAH females are mixed

10-3 Sexual Orientation

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Lesbians tend to show more masculine patterns of finger length

10-3b brain structure and sexual orientation ● ● ●

Several brain structures are sexually dimorphic, especially INAH-3 in the hypothalamus Lesions in INAH-3 in monkeys impairs heterosexual behavior but does not affect overall sex drive ○ INAH-3 was two to three times larger in heterosexual men than in homosexual men Anterior commissure, a small band of fibers connecting the two cerebral hemispheres, is known to be sexually dim ○ No direct role in sexual behavior ○ Observed differences may be due to an additional marker

10-3c genes and sexual orientation ● ● ●

Genetics appear to influence sexual orientation Chances of a homosexual male twin having a homosexual brother are 20-25% for fraternal twins and 50% for iden Genome-wide analysis of 409 pairs of homosexual brother identified two regions on chromosome 8 and the X chro sexual orientation

10-3d Sexual orientation and cognition ●

In one large-scale study using mental rotation tasks for assessing visuospatial skills, men consistently performed sexual orientation ○ Heterosexual men outperformed homosexual men, with bisexual men scoring between these two groups. ○ Homosexual and bisexual women scored at about equal levels, and both groups outperformed heterosexu

10-4 biological influences on adult sexual behavior ●

Activation of behavior by hormones is important to sexual behavior beginning at puberty and extends throughout th

10-4a The Regulation of Sex Hormones ● ●

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Hypothalamus exerts the most immediate control over endocrine system Manages the release of sex hormones through secretion of Gondaotropin-releasing (GnRH) ○ Light released by retina increases GnRH through action on melatonin ○ Melatonin- a neurohormone implicated in regulation of sleep and produced in pineal gland ■ Inhibits release of GnRH and light inhibits melatonin ○ Light INCREASES GnRH release by reducing inhibition normally produced by melatonin For other species lighter = producing offspring ○ Fertility times according to daylight hours ○ Human beings show some evidence of seasonality in birth rate ■ Sweden- spring-season baby boomlet GnRH travels to anterior pituitary gland ○ In response, anterior pituitary releases LH and FSH ○ Associated with the onset of puberty ○ LH signals testes to produce testosterone ○ LH and FSH control the menstrual cycle

10-4b Mood, Menstruation and Childbirth ●

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Premenstrual Syndrome: A condition in which some women experience physical and psychological symptoms im menstruation ○ Bloating and breast enlargement and tenderness ○ Psychological symptoms of depression and irritability ○ Severe cases: Premenstrual dysphoric disorder (PMDD): A condition in which premenstrual mood chan ○ More depression, changes in appetite (more calories ) and impaired cognitive performance disorder ○ Linked serotonin dysfunction with PMDD- treatment w/ SSRIs Postpartum Depression: A condition in which mothers who have recently given birth experience feelings of depr changing hormonal environment ○ Hormones shift from the pregnant state back to normal monthly cycles ○ Highest risk: younger than 20 yrs of age, unmarried, less educated & lower SES ○ Hist of being physically abused or using tobacco during last 3 months of pregnancy increases risk

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Can be predicted in 90% of patients as early as 3rd trimester from sensitivity to estrogen signaling

10-4c Hormones and Adult Sexual Behavior

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Sexual frequency of older men is correlated with testosterone levels Medroxyprogesterone acetate (MPA ; Depo-Provera) is used for contraceptive but also chemical castration doses) ■ Reduces circulating testosterone levels in men to prepuberty levels ■ Eliminates any sexual activity ○ Men in stable long-term marriages have lower testosterone levels ■ Being securely partner reduces testosterone ■ Perhaps due to lower levels of competition ○ Idea that reproductive situation affects hormone levels ■ Mens levels drop following birth of the child ■ Reflect a feedback loop in which decreases in testosterone follow reproductive success ■ High levels are not compatible with pair-bonding, parental care or immune system functioning Testosterone and Competition ○ Many environmental factors influence rapid changes in hormone levels ○ In both male & female athletes they increase in anticipation of a competitions ■ Will increase further in winners and decrease in losers ○ Even observing competition increases levels

10-5 Attraction, Romantic Love, Sexual Desire, and Parenting ● ●

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Viewing beautiful people is rewarding Young men in fMRI ○ Beautiful women activates pleasure & reward areas ■ Nucleus accumbens- also addictive behavior ○ Men could also press lever to see pictures of women ○ Willing to press the lever 6000 times in an interval of 40 minutes ■ Similar to amount of work rats would do to get cocaine Preference of beauty is evident at an early age Cultural factors influence this ○ 3 & 6 month old infants spend more time staring at faces adults had judged to be attractive than at faces ju

10-5a Elements of Physical Attractiveness ●

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Body symmetry ○ Highly symmetrical bodies are generally healthier ■ Some believe we are programmed to select healthy mates ■ View symmetry as attractive and beautiful ■ More opportunities for sexua activity ○ Symmetry appears to play a big role in the judgement of attractiveness in members of the opposite sex Preferred features ○ Males prefer features that reflect a natural attraction to younger females ■ Most likely to be fertile ○ Women's responses are not consistent ■ Some features preferred in short-term relationship but not long-term ■ Find more masculine men attractive as one night stands ■ Results from ability of women to recognize good genes ○ Testosterone is hard on the immune system so a man with high levels could not survive without an excelle ○ Balancing negative characteristics with masculine features ■ Men w/ more masculine faces would be more dominant, less faithful, worse fathers and have colde ■ Able to anticipate by simply looking at photographs ■ Might loos for less-masculine looking men for long-term partnerships b/c these men are assumed t more willing to invest in parenting Might be programmed to prefer males that smell a different way ○ Based on sweat ○ Mc...