sex. differences between males & females –anatomy (& its development) –physiology (e.g.,...
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sex
differences between males & females
– Anatomy (& its development)– Physiology (e.g., hormones)– Behavior (sexually dimorphic behavior)
Anatomy: A hermaphrodite is an organism that posses both male and female genitalia. Most common in invertebrates
– Simultaneous (slugs, earthworms)
– Sequential (clown fish)
'reclining hermaphrodite', a 1st-century BC sculpture
Anatomy: Sex determinationEvery 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)
Prenatal Hormones
Chromosomes
Gonads (testes)
Males
Internal genitalia
Chromosomal sex
Genital sex
Hormonal sex
Gonadal sex
Brain structures Brain sex
Y chromosome: Sry
External genitalia
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 ofMale internal and external genitalia
Internal Genitalia:Internal Genitalia
- Fallopian Tubes- Uterus- Inner Vagina
- Epididymis, vas deferens, - seminal vesicles, - prostate
External Genitalia:
- Clitoris,- Labia,- Outer vagina:
- Penis- Scrotum
Testosterone
Development of external genitalia in males
16-week old fetus
DHT(deihydrotestosterone)
5 alpha-reductase
Development of penis and scrotum
External Genitalia:
- Clitoris,- Labia,- Outer vagina:
- Penis- Scrotum
Sexual differentiation of the brain
TESTOSTERONE
ESTROGEN
aromatase
Masculinization of the brain
• Sensitivity to Test.osterone
• Spinal cord centers• Hypothalamic
differentiation• Defeminization
MALE
Sexual differentiation of the brain
TESTOSTERONE
ESTROGEN
aromatase
Masculinization of the brain
• Sensitivity to Test.• Spinal cord centers• Hypothalamic
differentiation• Defeminization
Circulating maternal estrogen? Attached to alpha-fetoprotein, does not get into the fetus brain
FEMALE
Prenatal Hormones
Chromosomes
Gonads (testes)
Androgen Insensitivity Syndrome
Internal genitalia
male
FEMALE
male
male
Brain structures
Y chromosome: Sry
External genitalia
No Receptors for Androgens
Prenatal Hormones
Chromosomes
Gonads (ovaries)
Adrenogenital Syndrome
Internal genitalia
female
MALE
male
female
Brain structuresExternal
genitalia
Androgen Hormone
Sex chromosomes abnormalities
Turner syndrome (X0) Klinefelter syndrome (XXY)