sex differences between males females Anatomy its development

sex

differences between males & females – Anatomy (& its development) – Physiology (e. g. , hormones) – Behavior (sexually dimorphic behavior)

'reclining hermaphrodite', a 1 st-century BC sculpture Anatomy: A hermaphrodite is an organism that posses both male and female genitalia. Most common in invertebrates – Simultaneous (slugs, earthworms) – Sequential (clown fish)

Anatomy: Sex determination Every grandma wants to know: “Will it be a boy or a girl? ” What determines the sex of the baby varies across species • Environmental – How hot it is (turtles, alligators) • Social – Is there a mom here? (clown fish) • Genetic – In humans & other mammals:

Sex determination systems XX XY Gamets (sperm & egg) are made by the gonads (testis, ovary) A sperm fertilizing an egg (ovum)

Males Chromosomal sex Y chromosome: Sry Gonads (testes) Gonadal sex Prenatal Hormones Brain structures Internal genitalia Genital sex External genitalia Hormonal sex Brain sex

Gonads: testis, ovary produce gametes (sperm, ovum) secrete hormones (testosterone; estrogen, progesterone).

Conception: Chromosomal sex is determined (XX, XY) 7 -8 weeks embryo: Undifferentiated gonads can develop into phenotypic male or female gonads Sry (a gene in Y chromosome): leads to male gonad development (testes) Hormones secreted by testes lead to development of Male internal and external genitalia

- Fallopian Tubes - Uterus - Inner Vagina - Epididymis, vas deferens, - seminal vesicles, - prostate - Clitoris, - Labia, - Outer vagina: Internal Genitalia: - Penis - Scrotum External Genitalia:

Development of external genitalia in males Testosterone 5 alpha-reductase DHT (deihydrotestosterone) Development of penis and scrotum 16 -week old fetus

- Clitoris, - Labia, - Outer vagina: - Penis - Scrotum External Genitalia:

Sexual differentiation of the brain TESTOSTERONE aromatase ESTROGEN Masculinization of the brain • Sensitivity to Test. osterone • Spinal cord centers • Hypothalamic differentiation • Defeminization MALE

Sexual differentiation of the brain TESTOSTERONE aromatase ESTROGEN Masculinization of the brain • Sensitivity to Test. • Spinal cord centers • Hypothalamic differentiation • Defeminization FEMALE Circulating maternal estrogen? Attached to alpha-fetoprotein, does not get into the fetus brain

Androgen Insensitivity Syndrome Chromosomes male Y chromosome: Sry Gonads (testes) male Prenatal Hormones No Receptors for Androgens Internal genitalia External genitalia Brain structures male FEMALE

Adrenogenital Syndrome Chromosomes female Gonads (ovaries) Prenatal Hormones female Androgen Hormone Internal genitalia External genitalia Brain structures MALE

Sex chromosomes abnormalities Turner syndrome (X 0) Klinefelter syndrome (XXY