Prep for Exam 2

Question 1

Organizational v Activational Effects

Answer 1

Organizational: active during development to modify structure or physiological function
- relatively permanent changes

Activational: active later in life to trigger or modulate behavior or seasonal expression of a trait

Question 2

Testosterone

Answer 2

• androgen (group of steroid hormones)
• male sex hormone synthesized in testes
• responsible for secondary male sex characteristics
• produced from progesterone

Question 3

Estrogen

Answer 3

• estrogen
• principle female sex hormone
• produced in ovaries
• responsible for secondary female sex characteristics

Question 4

Example of organizational effects

Answer 4

Rooster experiment
- examines the effects of castration and testicular replacement on appearance and behavior in the rooster

conclusion: testicles critical to sexual differentiation

Question 5

Sex Hormones and Behavioral Development

Answer 5

• males castrated as adults will respond to testosterone to facilitate male sexual behavior
• males will not respond to estradiol and progesterone facilitation of female behavior
• female pups injected with testosterone early in development will later respond to testosterone to facilitate male sexual behavior (masculinization)

Question 6

Summary

Answer 6

• early development determines masculinization or feminization of behavior (org. effects of testosterone)
• puberty is associated to activation of behavior (activational effects of testosterone)

Question 7

Chart

Answer 7

Ovary -> no testosterone -> feminization -> female behavior

Testicles -> testosterone peak -> masculinization -> male behavior

Question 8

What determines gonadal development?
(gonads are ovary/testis)

Answer 8

1. Genes on Y chromosome
2. SRY gene located on Y chromosome
3. SRY gene product (testis determination factor) determines the differentiation of gonads
4. Early testosterone critical to development of Wolfian ducts in males
5. Mullerian Inhibitory Hormone (by testis) inhibits development of Mullerian ducts in males

Question 9

Mullerian v Wolfian ducts

Answer 9

In males:
- testosterone promotes wolfian ducts
- mullerian inhibitory hormone: inhibits mullerian ducts

Question 10

Summary / Chart

Answer 10

XX -> ovary -> no testosterone -> feminization -> female behavior

XY (SRY gene on Y chromosome) -> testis -> testosterone peak -> masculinization -> male behavior

Question 11

Development of gender specific phenotypes (genitalia)

Answer 11

1. perinatal testosterone determines male genitalia (scrotum, penis) and phenotype
2. “default system” - no testosterone leads to the development of female genitalia (vaginal opening, clitoris) and phenotype
3. expression of SRY gene determines testicular development and male phenotype
4. Absence of testosterone means no wolfian duct system development = female phenotype
5. testicles also responsible for the production of anti-mullerian hormone inhibiting the mullerian duct system

Question 12

sexual phenotype development - males

Answer 12

T ——> DHT

• DHT activates androgen receptors
• masculinization of genitalia
• genitalia is androgen dependent - behavior is not

XY (SRY gene) -> testicle -> testosterone peak -> masculinization of behavior and masculinization of genitalia

Question 13

How does organizational effects determine behavior?

Answer 13

1. neural development
2. some brain areas are bigger in males while others are bigger in females
3. some neurotransmitters are more expressed in males, while others are more expressed in females (ex: kisspeptin) \
4. In males early peak of testosterone may affect trophic factors such as cell division, apoptosis (cell death), resulting in bigger structures

Question 14

Testosterone metabolism & DHT & 5-alpha

Answer 14

• testosterone cane be transformed into 5 alpha reductase
• DHT: male sex hormone that comes from testosterone in the body’s peripheral tissues
• in men, DHT binding to androgen receptors is responsible for facial hair
• The conversion of testosterone to DHT is primarily facilitated by the enzyme 5-alpha reductase.
• if enzyme is missing it can lead to sexual confusion, for example missing 5alpha in genitals will affect phenotype

Question 15

Testosterone metabolism & DHT & 5-alpha continued

Answer 15

• Testosterone can be transformed into DHT by 5-alpha reductase and then binds to androgen receptors in the brain and genitalia
• or testosterone can be transformed by aromatase to estradiol and bind to estradiol receptors in the brain
• in males, metabolism of testosterone into estradiol and 5-alpha plays a critical role in masculinization and defeminization

Question 16

Sexual differences and sex dimorphism

Answer 16

• sexual differences: giving men and women different hormones and looking at them
  example: increased androgen in women = increase facial hair and muscles
  example: castration of males and give them estrogen = change of appearance as well as more hips and increase of breasts
• sex differences are normally reversible

Sex dimorphism: irreversible for the most part
- castrate men rats at birth for example or give women rats androgen at birth
- can only be reversed by perinatal treatment

Question 17

Developmental mishaps and sex confusion

Answer 17

• in mammals, specific genes on the Y chromosome determine sexual differentiation of the gonads
• early androgen release perinatally determines sexual differentiation of external genitalia

Question 18

genital development thru SRY lens

Answer 18

Male Genitalia: In the presence of the SRY gene and testosterone, the indifferent gonads develop into testes, leading to the formation of male external genitalia (penis and scrotum) and internal reproductive structures (epididymis, vas deferens).

Female Genitalia: In the absence of the SRY gene and low levels of testosterone, the indifferent gonads develop into ovaries, resulting in female external genitalia (vagina, labia) and internal structures (uterus, fallopian tubes).