Sex: Evolutionary, Hormonal, and Neural Bases - 2nd half

What is sex determination?

The process by which a fetus is directed to develop as male or female.

What does the genital tubercle become?

The penis or clitoris.

What do the genital folds become?

The scrotum or labia

What can an indifferent gonad become?

Ovaries or testes.

Which duct system is associated with male internal development?

The Wolffian duct system.

Which duct system is associated with female internal development?

The Müllerian duct system.

According to the lecture, what determines sex during differentiation?

The hormones available before and after birth.

What are organizational effects of hormones?

Effects that set up or organize the system, mainly through androgens.

When do organizational effects occur?

During a sensitive developmental period.

What are activational effects of hormones?

Effects that activate an already organized system, such as at puberty or during sexual behavior.

What is behavioral defeminization?

Androgen effects that prevent an animal from displaying female-typical behavior.

What is behavioral masculinization?

Androgen exposure during a critical period that enables male-typical behavior.

What happens to a rat not exposed to androgens during the critical period?

It may behave like a female when given estrogen and progesterone.

What did the lecture note about female rats exposed to estradiol at birth?

They failed to show lordosis as adults.

What is the aromatization hypothesis?

Testosterone enters the brain and is converted to estrogen; these estrogens masculinize the developing rodent brain.

What role does a-fetoprotein have in the lecture material?

It is listed in the notes in the discussion of hormonal sex differentiation; no further function is specified.

What is the lecture's general statement about the placenta and aromatase?

The placenta typically uses aromatase to convert extra androgens into estrogens.

Why are female spotted hyenas discussed in relation to aromatase?

The notes say their placenta lacks aromatase, exposing females to more androgens and more male-typical characteristics.

What are examples of activational androgen effects at puberty?

Facial hair, voice change, hairline changes, increased muscle, and genital growth.

What are examples of activational estrogen effects at puberty?

Breast development, uterine lining growth, increased fat deposits, and maturation of genitalia.

Which hormone precursor is produced in the adrenal cortex in both males and females?

Androstenedione; it contributes to pubic and armpit hair.

What is sexual differentiation?

The development of male or female bodies and behaviors; in mammals it begins before birth and continues into adulthood.

When do gonads begin developing, and what are they called before then?

Around weeks 5–8; before then they are indifferent gonads.

What is the function of the gonads?

To produce gametes.

What is the default developmental pathway for indifferent gonads?

They develop into ovaries unless specific signals cause them to become testes.

What is the SRY gene?

The sex-determining region on the Y chromosome.

What does the SRY gene produce?

The SRY protein.

What does SRY protein do to the indifferent gonad?

It causes the inner core to proliferate, forming testes.

What hormones do developing testes secrete?

Testosterone and anti-Müllerian hormone (AMH).

What are gonadal hormones?

Hormones secreted by the gonads, mainly the testes, that direct sexual differentiation.

Which structures develop from the Müllerian system?

Fallopian tubes, the inner two-thirds of the vagina, and the uterus.

Which structures develop from the Wolffian system?

Vas deferens, seminal vesicles, and epididymis.

What happens to internal development without gonadal hormones?

The female-typical Müllerian system develops by default.

What is anti-Müllerian hormone (AMH)?

A hormone from the testes that causes Müllerian ducts to regress; it has a defeminizing effect.

What is testosterone's role in internal sexual differentiation?

It supports development of the Wolffian internal system.

What is dihydrotestosterone (DHT) responsible for?

Development of external male sex organs, including the penis and scrotum

What enzyme converts testosterone into DHT?

5-alpha-reductase.

What does 'nature's tendency to create a female' mean in the lecture?

Without the relevant testicular hormones, development follows the female-typical pathway.

What is Turner syndrome?

A condition involving a single X chromosome (XO), typically with 45 chromosomes.

How does Turner syndrome usually arise, according to the notes?

A sperm contributes no sex chromosome, leaving the individual with XO

How does a person with Turner syndrome typically develop sexually?

As female internally and externally, with absent or nonfunctional ovaries.

What characteristics associated with Turner syndrome are listed in the notes?

Short stature, sometimes a broader chest, a lower posterior hairline, and a higher incidence of being born blind; cognitive disability is noted as possible.

Why may estrogen be given at puberty in Turner syndrome?

With absent or nonfunctional gonads, ovarian hormone activation is reduced; estrogen may be used at puberty.

What is congenital adrenal hyperplasia (CAH), as described in the notes?

A condition in which the adrenal glands secrete too many androgens.

What can excess prenatal androgens cause in females with CAH?

An enlarged clitoris and partially fused labia; the notes describe this as intersex development.

Why are female internal organs usually present in CAH?

Androgens do not cause Müllerian duct regression, so female internal organs can develop

What effects on development are mentioned in the CAH notes?

Delays in the menstrual cycle and delays in marriage are reported in the notes.

What treatment approaches are listed for CAH?

Surgery after birth and cortisol injections; cortisol provides negative feedback that reduces further hormone release.

What is androgen insensitivity syndrome (AIS)?

A condition in which an XY individual cannot properly respond to androgens because androgen receptors do not function.

How does AIS affect internal reproductive development?

AMH causes Müllerian regression, but nonfunctional androgen receptors prevent Wolffian development.

How do individuals with AIS typically appear externally?

They typically have female external anatomy and a female phenotype

What puberty-related features are described for AIS?

Breast development occurs, but menstruation and axillary or pubic hair development do not.

Why does menstruation not occur in AIS, according to the developmental pathway in the notes?

The Müllerian system regresses, so a uterus is absent.

What is the lecture's explanation of why individuals with AIS do not develop pubic or axillary hair?

They cannot respond to androgens.

What is the genetic pattern in guevedoces?

XY.

What causes guevedoces?

A genetic mutation affecting the enzyme 5-alpha-reductase.

Why may typical male external genitalia not form before puberty in guevedoces?

Without normal 5-alpha-reductase activity, testosterone is not converted effectively to DHT.

What change may occur at puberty in guevedoces?

Testosterone-driven masculinization occurs and the penis begins to grow.

How are guevedoces often raised in childhood, according to the notes?

They are usually raised as females

What is cloacal exstrophy?

A serious developmental disorder in which genetic boys may be born with testes but without a penis.

What sex may be assigned at birth in the cloacal exstrophy example?

Female; long-term outcomes vary, with some accepting and others rejecting that assignment.

What two broad classes of influences on sexual orientation are listed?

Societal instruction and endogenous factors, especially varying levels of fetal testosterone.

How might fetal testosterone influence later behavior, according to the notes?

It may organize the developing brain and affect future behavior

Is same-sex sexual behavior observed in nonhuman species?

Yes. The notes give examples in wild animals, especially sheep

What behavior was observed in some wild rams?

Some rams do not mount females but choose to mount other males.

What brain difference was reported in the sheep studies?

Rams mounting females had a masculinized preoptic area; rams mounting males did not.

What brain structure did Simon LeVay examine?

The third interstitial nucleus of the anterior hypothalamus (INAH-3), part of the preoptic area.

What did LeVay report about INAH-3 size?

It was larger in males than females; in ho

What were two limitations or criticisms of LeVay's research noted in class?

The study included only males, and many brains came from people with HIV, which can affect the brain.

Why did LeVay want to investigate brain differences

He wanted to provide evidence that sexual orientation was not simply a choice.