Presentation on theme: "(and other animals) become male or female?"— Presentation transcript:
1 (and other animals) become male or female? How do we(and other animals) become male or female?
2 Sexual Differentiation: Overview Sex DeterminationThe event that determines whether an individual will become male or femaleSexual DifferentiationThe developmental process of becoming male or female
3 Sexual Differentiation: Overview What is Sex?• Chromosomal sex• Gonadal sex• Gametic sex• Hormonal sex• Morphological sex• Behavioral sex• Gender identity• Gender role• Legal sex
4 Sexual Differentiation: Overview Jost’s Model of Sexual Differentiation:
5 What determinesgonadal sex(development oftestes vs. ovaries)?
6 Gonadal Differentiation Nelson 2005 Fig. 3.4Germinal ridge:• Thickened ridge of tissue on surface of each mesonephros (protokidney)• Can develop into a testis or an ovary
7 Gonadal Differentiation: SRY Gene (Sex-Determining Region of Y Chromosome)TDF binds to DNA and regulates genescontrolling development of testes
8 Gonadal Differentiation: SRY Gene Evidence for role of SRY gene:• SRY is activated shortly before gonads differentiate.• XY phenotypic females often have mutations in SRY (humans, mice).• XX phenotypic males often have SRY-containing translocation to X chromosome.
9 Gonadal Differentiation: SRY Gene Evidence for role of SRY gene:• SRY is activated shortly before gonads differentiate.• XY phenotypic females often have mutations in SRY (humans, mice).• XX phenotypic males often have SRY-containing translocation to X chromosome.• XX transgenic mice: introduction of SRY causes testicular development.BUT: Autosomal genes also contribute totestis development.
10 Gonadal Differentiation: Ovary-Determining Genes • Unclear if any exist.• Have been hypothesized to exist and to be switched off in males by activation of SRY gene.• Two X chromosomes necessary for normal ovarian development.
11 Gonadal Differentiation • Germinal ridge is initially indifferent/bipotential.• TDF expression no TDF expression • TDF acts locally – not blood-borne.• In mammals, sex steroids have limited effects.Human fetalovariesHuman fetaltestes
12 of the internal reproductive tracts? What determinesdifferentiationof the internal reproductive tracts?
17 of the external genitalia? What determinesdifferentiationof the external genitalia?
18 Differentiation of External Genitalia Nelson Fig. 3.7
19 Differentiation of External Genitalia • Bipotential anlagenGenital folds, genital tubercleIdentical in males and females until week 6-8• Effects of androgens (males)Genital tubercle penisGenital folds scrotum (testes descend later)• Absence of androgens (females)Genital tubercle clitorisGenital folds labia
20 Summary of Sexual Differentiation Silverthorn Table 26-1
21 ANOMALIES OF SEXUAL DIFFERENTIATION What can go wrong, andwhat do the exceptionstell us about the rules?
22 True Hermaphroditism• Both ovarian and testicular tissue are present in the same individual– ovary on one side, testis on the other– “ovotestes”• Uncommon• Usually 46,XX; sometimes 46,XX/46,XY chimerism or mosaicism• Phenotypically variable• Some are fertile as females
23 Anomalies in Chromosomal Females: Turner Syndrome (XO) • Gonadotropin levels: high in infancy and post-pubertally; normal prepubertal hiatusImmature genital tract & external genitals; short stature• Often lethal prenatally
24 Anomalies in Chromosomal Females: Turner Syndrome (XO) Wilson & Foster 1987 Fig
25 Anomalies in Chromosomal Females: Congenital Adrenal Hyperplasia (CAH) • Causes masculinization of the external genitalia in females.• Can be mild to severe.• Can be treated with surgery and exogenous steroids.
28 Anomalies in Chromosomal Females: Congenital Adrenal Hyperplasia (CAH) Wilson & Foster 1987 Fig
29 Anomalies in Chromosomal Males: Androgen Insensitivity Syndrome (AIS) (Testicular Feminization (TFM))• Testes develop; Wolffian and Müllerian ducts regress; external genitalia appear female.• Female body type and gender identity, but sterile.
30 Anomalies in Chromosomal Males: 5a-Reductase Deficiency (Guevodoces, Penis at Twelve)• No 5a-reductase – can’t convert T to DHT.• XY infants have ambiguous genitalia and small, undescended testes.5a-Reductase5a-Dihydro-testosterone (DHT)H517-beta Estradiol(E2)Aromatase17ATestosterone (T)19
31 Anomalies in Chromosomal Males: 5a-Reductase Deficiency (Guevodoces, Penis at Twelve)
32 Anomalies in Chromosomal Males: 5a-Reductase Deficiency (Guevodoces, Penis at Twelve)
33 Anomalies in Chromosomal Males: Trisomies1. XXY (Klinefelter Syndrome)Phenotypically maleSmall testes, androgen deficiency, low sperm production (sterile)GynecomastiaLow intelligenceNelson 2005 Fig 3.14XXYXYY2. XYYPhenotypically maleNormal sexual developmentExtremely tallLow intelligence, HyperactiveAntisocial
Your consent to our cookies if you continue to use this website.