2. Sexual Determination and Differentiation

Question 1

Girls and boys are different

Answer 1

Reproductively and behaviorally

Question 2

What causes these differences?

Answer 2

Nature AND nurture

Biology AND environmental factors (learning, society, culture)

Question 3

Strategies to explore questions about the origin of human behavior

Answer 3

Studying sexual differentiation in animal models

Studies of people or animals with anomalous development

Sampling amniotic fluids and correlating hormone levels with later behaviors

Looking for universal commonalities in the behavior of all children

Question 4

Where else do we see sex differences?

Answer 4

Aggression
Cognition
Mental health disorders
Cardiovascular and immune function

Question 5

The gonads serve 2 purposes

Answer 5

Production of gametes
Production of steroid hormones

Question 6

Steroid hormones are required for:

Answer 6

Gamete production, development of secondary sex characteristics, behaviors that bring gametes together

Question 7

Male gonads: testes

Answer 7

Primary steroid produced is testosterone, which is an androgen

Testosterone production begins as soon as the testes are formed

Question 8

Female gonads: ovaries

Answer 8

Primary steroids produced are estrogens (ex: estradiol) and progestins (ex: progesterone)

Steroids are not produced from the ovaries until puberty

Question 9

Sex determination

Answer 9

The process by which the decision is made for a fetus to develop as a male or female

Chromosome driven

Question 10

Sex differentiation

Answer 10

The process by which individuals develop either male or female bodies and behaviors

Hormone driven

Question 11

Mammalian sexual determination

Answer 11

If the sperm that enters the egg has a Y chromosome, the offspring is male; if an X, the offspring is female

Question 12

“Male” and “Female” hormones

Answer 12

No steroid is found exclusively in either males or females; rather, the two sexes differ in the proportion of these steroids

Question 13

Levels of sex determination/differentiation

Answer 13

Question 14

When the fetus is first made

Answer 14

6 weeks of gestation- gonads first made

They’re bipotential: the same gonad can become either testes or ovaries

Question 15

SRY gene

Answer 15

The Y chromosome has the SRY gene (sex-determining region of the Y chromosome) which codes for testes

Without SRY gene, an ovary forms

Question 16

Sex differentiation driven by hormones

Answer 16

Hormones secreted by gonads, mainly from the testes, direct sexual differentiation of internal and external sex organs

Question 17

Hormonal sex differentiation in males

Answer 17

In males, the Wolffian ducts develop into the epididymis, vas deferens, and seminal vesicles, and the müllerian system shrinks

Question 18

Hormonal sex differentiation in females

Answer 18

In females, the müllerian ducts develop into the oviducts, uterus, and vagina– the Wolffian system degenerates

Question 19

2 hormones produced and released early on in males:

Answer 19

Anti-müllerian hormone (AMH) causes regression of the müllerian system

Testosterone masculinizes the internal organs by promoting development of the Wolffian system

Question 20

Testosterone gets converted into…

Answer 20

Dihydrotestosterone (DHT) via the enzyme 5a-reductase masculinizes external structures

Question 21

Testosterone aromatized to ________ via aromatase– masculinizes the brain

Answer 21

Estradiol

Question 22

Chromosomal anomalies

Answer 22

Turner’s syndrome
Klinefelter’s syndrome

Question 23

Turner’s syndrome

Answer 23

A person only has one sex chromosome, a single X

The individual develops as a female, due to lack of SRY gene, with abnormal ovaries (no steroid hormone production or eggs)

Estrogen treatment induces breast growth and a female-typical puberty

Question 24

Klinefelter’s syndrome

Answer 24

A person has an extra chromosome, XXY

A masculine body develops because of the Y chromosome

Testes and penis are abnormally small

Low testosterone production; little to no sperm are produced

Question 25

Hormonal anomalies

Answer 25

Congenital adrenal hyperplasia (CAH)
Androgen insensitivity syndrome

Question 26

Congenital adrenal hyperplasia (CAH)

Answer 26

Can happen in XX or XY individuals
Lack enzyme (21-hydroxylase) that produces cortisol, results in increased amount of androgens output from adrenal gland

External genitalia is partially masculinized because of exposure to increased DHT during development
Internal organs are mostly normal

The females exhibit more masculine behaviors
Affected individuals need to keep taking cortisol throughout their lives

Question 27

Androgen insensitivity syndrome

Answer 27

Occurs in XY people with defective androgen receptors (so, androgens cannot have action)

Question 28

Will people with androgen insensitivity syndrome develop testes or ovaries?

Answer 28

Testes, because of the SRY gene on the Y receptor

Question 29

What hormones will be produced in people with androgen insensitivity syndrome? Which will act?

Answer 29

WILL act: AMH and estradiol (because they’re not androgens)

WON’T act: testosterone and DHT (because they’re androgens)

Question 30

What will be the phenotype of an individual with androgen insensitivity syndrome?

Answer 30

Female, because the testes stay internal and DHT cannot create male genitalia
Internalized testes, no eggs, shallow vagina

T is low, so estradiol stays low and brain is not masculinized

The women use hormone therapy

Question 31

Sexual dimorphism

Answer 31

The condition in which males and females exhibit marked sex differences in appearance

POA in hypothalamus is important for reproductive behavior in males

Question 32

masculinization or feminization of the brain

Answer 32

Estradiol masculinizes the brain during early development

This occurs (primarily) in males, since ovaries don’t produce hormones until puberty

Question 33

activational effect of hormones

Answer 33

Temporary
Occurs in adulthood

Question 34

organizational effect of hormones

Answer 34

Structural changes in brain
Permanent
Occurs before brain matures
Critical period

Question 35

Females do not become masculinized during fetal development because…

Answer 35

Ovaries are quiescent until puberty
Maternal estrogen in developing females does not enter the brain

α-fetoprotein binds the estrogens, keeping them from crossing into the brain, thus preventing aromatization and masculinization