sex differences

topic 1

sex

talks more about the biological aspects (gender = more cultural)

what is XX

WOMEN

what is XY

MALE

sex determination in mammals through the gene SRY involves

turning the fetal gonad into a testes - its the testes determining factor

in its absence the gonad becomes ovary

sex determination in mammals through hormones involves

early testes producing - anti-mullerian hormone (defeminising) and androgens (masculinising)

without these hormones the female sex organs will develop. the genitalia will develop female

what is the mullerian system

precursor to female system

what is the wolffian system

precursor to the male sex organs

what is the wolffian system maintained by

maintained by the androgens when androgens bind to their receptors and allow for the system to continue existing and become male internal genitalia

what happens to the wolffian system when there are no androgens

the wolffian system dissappears and the female internal sex organs are developed from the mullerian system

how is the mullarian system removed

if the testes is formed and the anti-mullarian hormone is produced then then mullarian system is disintergrated

sex determination in mammals through external sex organs

they start completely undifferentiated.

after the gonad is turned into either testes or ovaries the external genitalia are sensitive to androgens ( DHT) made by the testes.

DHT is required to turn the external anatomy into male specific like scrotum and penis.

if no DHT then we get female specific anatomy. what would be the scrotum becomes the labia.

what is persistent mullerian duct syndrome

person has external male genitalia, wolffian system is working fine but there is no anti-mullerian hormone so they have the start of a uterus.

they have both male and female internal genitalia

what are the organisational actions of hormones

effects remains after the hormone has been removed often occurs during a sensitive period. if you take the testosterone away from a boy they wont lose the internal and external genitalia these changes are permanent.

wide pelvis in women cannot be undone when they have occured

what are activational actions of hormones

effects if reversible depending on presence or absence of hormone. take hormone away the effect goes away.

when does puberty occur

at some point in teenage year

producing horomones and become sexually mature

what is the onset of puberty

during childhood - sex hormone levels are undetectably low

developmental timing mechanism starts puberty

sex differences in mechanism and timing

GnRH - during puberty

in the hypothalamus neurons called GnRH neurons that normally trigger a cascade of to release sex hormones. during childhood they dont release hormone called GnRH as these neurons are being inhibited by GABA.

during puberty you get activation of kisspeptin neurons and inhibition of GABA.

GnRH definition

Gonadotropin releasing hormone

hormone released into the blood. it effects the testes and ovaries production of hormones

hypothalamus, pituitary gland and GnRH

released into the small blood vessels which feeds into the anterior portion of the pituitary gland. where other cells have receptors for GnRH which will in turn start making their own hormones which goes to the gonads

gonadotropins are released.

what are gonadotropins

hormones whos target is the gonads

what does LH do

stimulates the production of testosterone from different set of cells in testes

in females LH causes ovulation

MALES - what occurs in the feedback system of the hypothalamus-pituitary gonadal axis

simple negative feedback system

HPG axis in males is a negative feedback system that keeps testosterone around a set point. if it is below in the blood then the hypothalamus GnRH will release to increase gonadotropins LH and release testosterone opposite if too much

if the male takes anabolic steroids the consequences on the HPG axis include the hypothalamus produces less GnRH testes make low amounts of testosterone and the testes will shrink.

FEMALES - the menstrual cycle and ovulation

at the end of the cycle there is an increase in FSH from the anterior pituitary gland in the bloodstream. this will bond to the follicles in the ovary one of those follicles will being to ripen.

from day 5-13ish the follicular phase occurs - producing oestradiol. when this reaches a certain level it crosses a threshold which will trigger GnRH in the hypothalamus to release LH and FSH.

peek of LH and FSH triggers ovulation - follicle is now called corpus luteum

this starts making oestradiol and progesterone which until now has been low. this stats building up the uterine lining ready to receive implantation of embryo.

variation in sexual differentiation - androgen insensitivity syndrome

the body isnt sensitive to androgens - the receptors dont work properly

gonads develop as testes - anti-mullairan hormones work fine

androgen receptors dont work - testosterone cant do its job

XY develop anatomically female but no female internal genitalia.

XX lack of public hair they have ovaries and female hormones - chances are they wont know they have it

puberty is typically late

people with it typically identify as female

variation in sexual differentiation - 5alpha - reductase deficiency

5 a reductase turns testosterone into DHT - DHT is crucial for prenatal external genital development

XY born with female external genitalia by male internal when they hit puberty they develop a penis

“guevedoces” - common in Dominican Republic call people penis at 12.

after puberty most identify as men

variation in sexual differentiation - congenital adrenal hyperplasia

21- hydroxylase deficiency

high levels of prenatal testosterone in girls - often treated when diagnosed.

XX assigned male at brith

5% of CAH girls assigned female at birth have gender dysphoria

12% of CAH “girls” assigned male at birth have gender dysphoria

hypothalamus-pituitary adrenal axis - CAH

the adrenal gald makes cortisol. 21-hydroxylase makes cortisol which is important as its involved in energy balance.

people with this struggle with symptoms of low cortisol as the precursor to cortisol become testosterone not cortisol. you get some of the primary sexual characteristics of males during embryonic development as a female

activational hormone effects on origins of sex differences in brain

variations with varying testosterone, oestradiol levels.

no differences detected in adulthood between sexual orientations

hormone fluctuations manipulation or treatments affect sexual motivations

hormone activation are the cause of many sex differences but not sexual orientation

gynophile

attraction to women

androphile

attraction to men

O.H - what are the r periods where testosterone is high in boys

8-24 weeks pregnant - early external genitalia, late - brain differentiation

first 3 months after birth - potential further brain differentiation

O.H correlates of embryonic testosterone - cognitive performance

verbal abilities are better in androphile men than gynophilic men

visuo-spatial performance is worse in androphile men than gynophile men

mental rotation is faster in gynophile women than in androphile women

all very tentative evidence

O.H - correlates of embryonic testosterone - ratio of 2nd and 4th finger lengths

sex differences in 2D/4D ratios = male - 0.95 female = 0.97

in females they are more similar lengths than that of men - on average men have shorter index fingers.

gynophile women - butch lesbians have more masculine 2d-4d ratios and are more masculine presenting suggesting more testosterone in development

no consistent findings in androphile men

O.H- correlates with embryonic testosterone - oto-acoustic emissions

when stimulated with a click the ears make a click back. this is louder and more frequent in women.

early t development in other species

gynophile women closer to gynophile men than androphile women

genetic effects for sex differences - twin studies

high concordance rates in mz than dz

estimates 30-100% - lower end more likely as there is more bias higher

possibly higher concordance for women than men.

genetic effects for sex differences - genetic mapping

androphile men more often have androphilic maternal uncles.

a region of the X chromosome has been identified as related to sexual orientation

genetic effects of sex differences - concerns from evolution standpoint

should homosexuals have less offspring?

how does a putatuve genetic basis not get selected out of the population.

possible mechanisms for maintaining such genes

• heterozygotic advantage

• kin selection

• different effects in male and female.

genetic effects in sex differences - fraternal birth order effect

the odds of having a boy that is androphilic increases the more boys youve had as a mother - the more older brothers by the same mother the more likely the boy will be gay. sisters dont have an effect.

sexual orientation conclusions

clear biological developmental influences. no influences is absolute sexual orientation can be influence by several different factors

what is gender identity

has even larger sex differences than sexual orientation - doesnt seem to be binary

childhood gender dysphoria doesnt always continues after puberty - does for 40%

study looking at transgenders

genetic mapping was done and it was found that it seems like there are genes that are associated with gender dysphoria

for FTM having the long version of the oestrogen receptor alpha and the oestrogen receptor beta made more correlated with being trans.

there is enough of an association that there is something to connect them with effecting gender identity.

pre-transition brain differences

brain volume are in lines with natal sex

MTF individuals shown more feminine cortical thickness and white matter in some brain areas.