(E1, L3) Sex Determination and Differentiation Pt. 1

Question 1

What is sexual determination?

Answer 1

The process by which an organism is originally set up to become either male or female

Question 2

What is sexual differentiation?

Answer 2

-The process during development through which an individual becomes either male or female
- The process of males and females developing (slightly) different brains, bodies and behaviors (complicated process)

Question 3

What is sex?

Answer 3

biological, the physical body
- essentially the “biological and physiological characteristics that distinguish females from males”

Question 4

What is gender?

Answer 4

social concept, self-identification
- “socially constructed roles, relationships, behaviors, relative power, and other traits societies ascribe to women and men”

Question 5

Is sex a dichotomy?

Answer 5

nope, its a spectrum
Composed of:
- who you’re attracted to
- what sex you identify with
- chromosomal make-up
- appearance of external genitalia
(sometimes there is concordance among these, sometimes individual traits are male-like and some are female-like)

Question 6

What are some strategies to explore the questions about human behavior origins?

Answer 6

1. Studying sexual differentiation in animal models
2. Studies of people or animals with anomalous development (congenital adrenal hyperplasia, or CAH)
3. Sampling amniotic fluids for hormone concentrations and correlating it with later behaviors
4. Looking for universal commonalities in the behavior of all children

Question 7

How does the XY genotype lead to male development?

Answer 7

The XY chromosomes set up the gonadal sex and therefore testes. These testes secrete testosterone which in turn creates estradiol and DHT. These work to develop and organize the brain and external sex characteristics (morphological sex), resulting in the behavioral sex.

Question 8

How is sex determined?

Answer 8

The SRY gene (sex-determining region on the Y chromosome) codes for testes to develop from bipotential gonad (which can go both ways)

Question 9

How is the Mullerian duct system created? At what stage is it developed?

Answer 9

• precursor of female accessory sex organs
• regresses in the presence of testes because of te production of anti-Mullerian hormone (AMH; or Mullerian inhibitory hormone, MIH)

Question 10

What is the Wolffian duct system?

Answer 10

• precursor of male accessory sex organs
• Develops in the presence of testes because of testosterone (T)

Question 11

What hormones are involved in sexual differentiation?

Answer 11

Testosterone is present in the testes and masculinizes internally
- 5alpha-Reductase present –> T becomes 5alpha-DIhydrotestosterone (DHT) –> masculinizes externally
- Aromatase is present –> T becomes Estradiol –> helps in masculinizing the brain during organizational stage

Question 12

Describe in detail the sex determinism and differentiation of the XY chromosome.

Answer 12

Determinism–>XY chromosome expresses SRY gene
Differentiation–> AMH and T released
-AMH causes mullerian ducts to regress
-T induces Wolffian ducts to form internal sex organs, prostate and gonads
-5alpha-reductase is present –> T becomes DHT –> development of external male sex organs

Question 13

Describe in detail the sex determinism and differentiation of the XX chromosome.

Answer 13

Determinism–>XX chromosome; no SRY gene
Differentiation–> Ovaries produce no AMH, no T, becomes feminized
- In absence of AMH, Mullerian ducts form internal sex organs
- In absence of T, Wolffian ducts regress
- in absence of DHT, external female sex organs deverlop

Question 14

Explain the continuum of the accessory sex organs during development

Answer 14

-Masculinization: creates the male sex organs
-Feminization: creates the female sex organs
-Demasculiniation: removes the capability to have male sex organs
-Defeminization: removes the capability to have female sex organs

Question 15

What is important to note about these hormones in early sex development?

Answer 15

-The early exposure to hormones is changing the body AND the brain (driven by estradiol)
- This means brain regions, circuits, neuron number and density are being organized in a male or female specific way
-this affects a variety of behaviors in adulthood

Question 16

How is hormonal exposure early in development different from later in adulthood?

Answer 16

-Gonadal hormones have organizing, or programming effects, upon brain and behavior during development
-Hormone exposure later in life results in reversible, short-acting behavioral influences

Question 17

What are the organizational effects of gonadal steroids?

Answer 17

the influence of gonadal steroids during CNS development shapes that development and thus has a lasting effect on male and female brain organization and, hence, behavior (happens in development/critical period)
(structural changes in brain, permanent, occurs before brain matures, critical period)

Question 18

What are the activational effects of gonadal steroids?

Answer 18

gonadal steroids interact with (or activate) fully developed brain structures to shape behavior. The brain is NOT changed here, but the way ti controls behavior is. (happens in puberty and beyond)
(biochemical changes, transitory, occurs in adulthood, no sensitive period)

Question 19

Explain what would happen when estradiol is introduced to a female rat within the critical period and then again what behaviors would she display when exposed to either testosterone or estradiol + progesterone.

Answer 19

Estradiol in critical period: masculinized and defeminized brain
Testosterone at puberty: male sex behavior
Estradiol at puberty: no sexual behavior (because we have removed her capabilities for it in the critical period)

Question 20

Explain how testosterone alters gene expression in the prenatal brain

Answer 20

1. Testes release the androgenic hormone T into bloodstream
2. T molecules enter neurons in the brain
3. They are met with the aromatase enzyme and converts the T into estradiol
4. Estradiol binds to the estrogen receptors which complex binds DNA in the nucleus
5. this increases transcription of some genes and decreases it in others. it may also prevent or promote apoptosis

Question 21

What is aFP? How does it work?

Answer 21

a-fetoprotein are bind estrogen molecules in circulation, many of which are from the mother’s ovary and hold onto them until they can be metabolized by the liver.
T is free to make it into the cell in male rats to masculinize the brain.
There is only so much aFP, so if the mother’s ovaries produce enough estrogen, the molecules can overwhelm the aFP present and get into the neuron to defeminize the brain.

Question 22

What are the effects of intrauterine position within rats?

Answer 22

• Female rats that develop between 2 males are less sexually receptive to males and more aggressive as adults–this is due to their increased exposure to T (which bypasses the AFP receptors and can aromatize to estradiol to masculinize the brain)

Question 23

How can we have four different core genotypes? What are they?

Answer 23

Scientists can remove the SRY gene from the Y chromosome, or add the SRY gene to another autosome (a chromosome that’s not a sex chromosome)
- in this way, we can get genetic males (XY) that are hormonally female (because they lack the SRY gene)
- and we can get genetic females (XX) that are hormonally male (because they have the SRY gene)
- and the others are hormonally the same as their chromosomal sex (male and female)

Question 24

What are the names of the core genotypes?

Answer 24

Female XX: genetic female with overies
Male XY: genetic male with testes
Female XY-: genetic male with ovaries
Male XX SRY: genetic female with testes
Male XY- SRY: genetic male with testes (control for removing the SRY gene)