sex differentiation and determination Flashcards
chromosomal sex
XX= female XY= male
determined by sex determination: fertilization of ovum by sperm bearing a X or Y chromosome
point at which an individual develops as a male or female
gonadal sex
presence of ovaries (F) or testes (M)
germinal ridge
primordial gonad that is indifferent/bipotential–> aka it has the potential to develop into either an ovary OR testis
hormonal sex
sex of an individual determined by the concentration/ratio of androgens to estrogens
morphological sex
sex determined by body form
- accessory sex organs/internal structures
- external genitalia
- secondary sex characteristics
Mullerian duct system
develops into FEMALE accessory sex organs (fallopian tubes, vagina, cervix, uterus)
**development of Mullerian progresses w/o presence of local testosterone, and lack of MIH
Wolffian duct system
develops into MALE accessory sex organs (vas deferens, seminal vesicles, epididymis, prostate)
- *development of Wolffian dependent on LOCAL TESTOSTERONE (masculinization)
- *regression of Mullerian (F) dependent on MIH (defeminization)
male external genitalia development
- *blood borne testosterone, 5a reductase
- *testosterone–> DHT
- *DHT needed for male penile and scrotal development
female external genitalia development
**lack of androgens/absence of testosterone–> labia and clitoris
Turner syndrome
XO
- female external appearance
- limited ovarian development, gonads not fully developed
- do not produce steroid hormones
- hormone therapy needed to undergo puberty
- short, webbed neck
Klinefelter syndrome
XXY
- externally and internally masculinized
- SRY gene activation from the Y chromosome–> masculinization
- sterile b/c of decreased sperm production
- tall, long
- underdeveloped penis
- gynecomastia: boob growth
gynecomastia
boob growth seen in individuals with Klinefelter’s syndrome
Jacob’s syndrome
XYY
- male, may be sterile
- associated with increased aggressiveness
- taller, lesser intelligence
- elevated testosterone
congenital adrenal hyperplasia
XX
- enzyme deficiency: 21-hydroxylase
- continuous secretion of androgens–> early androgen exposure (blood borne–because there is no Y chromosome, there is no testis–> no local testosterone–> no Wolffian development; and with no MIH, Mullerian system develops normally)
Mullerian system develops normally
external genitalia: because of elevated blood borne androgen in the adrenal cortex–> genitalia will be AMBIGUOUS
21-hydroxylase role
cholesterol–> pregnenolone–> progesterone–> aldosterone and cortisol (mineral corticoid and glucocorticoid steroid hormones)
–progesterone–> ald. and cort. via 21-hydroxylase
cholesterol–> progesterone–> androgens
21-hydroxylase deficiency implications
if 21-hydroxylase isn’t working, there will be no negative feedback on CRH (corticotropin releasing hormone) and ACTH from the anterior pituitary–> increased levels of CRH and ACTH–> increased stimulation of the adrenal cortex (trying to produce glucocorticoids and mineral corticoids)–> increased synthesis of ANDROGENS–> masculinize and defeminize the fetus
androgen insensitivity syndrome= testicular feminization
- XY
- lack of androgen receptors (you have androgens, but there are not going to produce a biological effect)
- MIH: regression of the Mullerian system
- testosterone but no receptors: regression of Wolffian
- no internal structures
- b/c there are no androgen receptors–> feminized external genitalia
- female behavior
- infertile (often discover they have AIS because they do not have a period)
5-a reductase deficiency
- 5a reductase implicated in conversion of testosterone–> DHT (directly responsible for male external genitalia development)
- XY–> SRY gene–> testes–> testosterone–> Wolffian
- NORMALLY: testosterone–> DHT (penis and scrotum); but w/ deficient 5a reductase, genitalia are AMBIGUOUS
- MIH: regression of Mullerian system
- increased testosterone production during puberty–> masculinization
- can lead to hypospadias
hypospadias
urethral opening that is not at the tip of the penis
-seen during puberty in ind w 5a reductase deficiency
organization/activational hypothesis
in development (during a critical period), sex hormones “organize”/program the nervous system and structures needed for male and female behaviors
Organization: occurs early during a critical period in development, is permanent and irreversible
in adulthood, sex hormones activate/inhibit/modulate the function of neural circuits
Activation: occurs peri-pubertal or later, is short term and is reversible
early hormone environment during a critical period ORGANIZES the brain, hormones in adulthood ACTIVATE brain and behavior
(lordosis requires activation by estrogen and progesterone, mounting requires activation by testosterone)
Young experiment
Question: how are behavioral differences in hormonal responses between males and females mediated?
Hypothesis: Hormonal events early in development are responsible for the induction of male and female behavioral patterns
procedure:
- injection of testosterone propagate into pregnant guinea pigs during pregnancy
- adulthood: androgen exposed males and females (as well as control males and females) gonadectomized and injected with estrogen and progesterone
results
-females who had been treated with androgens had DECREASED LORDOSIS, INCREASED MOUNTING
(androgen exposure programmed male behaviors)
-males treated with androgens were not impacted (normal mounting, no lordosis)
conclusion: prenatal action of hormones in causing differentiation/organization of neural substances for behavior
feminization, masculinization
feminization: absence of exposure to gonadal steroids
masculinization: begins when testis produces androgens during a critical period
gonadal hormones increase in adulthood–> promotion of sex difference sin behavior by acting on a neural substrate that was organized during the CP
LH release in male and female rats
GnRH (hypo)–> LH (AP)
During ovulation, a surge of estrogen–> surge of GnRH–>surge of LH and FSH–> ovulation via positive feedback mechanisms
anosmic
cannot smell
uterine position and early androgen exposure effects
exposure to androgen secreted by male littermate MASCULINIZES and DEFEMINIZES female pups
0M and 2M have the same reproductive capacity BUT…
- intrafemale aggression: 2M>0M
- time males spend with females: 0M>2M
- length of ovarian cycle: 2M>0M
- ease of inhibition of cycle by other females: 0M>2M
estradiol and aromatization
testosterone–> estradiol via aromatase
-masculinizing effects of testosterone exerted through the brain by conversion by aromatase into enzymes
a-fetoprotein
binds to estradiol so that it cannot enter the brain and exert masculinizing effects
DNMT
testosterone removes ___–> removal of a methyl group–> gene transcription–> masculine behaviors in adulthood
lack of testosterone–> methylated proteins (DNMT NOT REMOVED)–> silencing of gene transcription
DNA methylation
epigenetic mechanism of gene regulation whereby methyl groups are added to DNA to decrease gene transcription
if females are given DNMT inhibitors… NO METHYL–> gene transcription allowed–> masculinized behavior in adulthood
conclusion: masculinization requires DEmethylation, feminization requires METHYLation
sexually dimorphic nucleus of POA
males: SNN-POA much larger b/c testosterone/estradiol protects neurons from apoptosis
females treated prenatally w/ androgens have a much larger SDN-POA
males castrated prenatally/during CP–> F-sized SDN-POA
