topic 2 - sex differences Flashcards
gene SRY
located on Y-chromosome
turns fetal gonad into testis
- testis-determining factor
- if not there, gonad turns into an ovary
hormones early testis produce
Anti-mullerian hormone (defiminsing)
- anrogens (masculalinising)
in abscence of these hormones - female sex organs develop.
organisational hormone effect
effect remains after the hormone has been removed, often occurs during sensitive period
activational hormone effect
effect is reversible, depending on presence or absence of hormone
nuerons that are responsible for the onset of puberty
GnRH nuerons
how does puberty start
GABA/NPY neurons are shut down, activating the KNDy neurons which then triggers the release of GnRH - 2 hour pattern
what happens when GnRH is released
it is released into the capillaries in the pituitary gland.
When the anterior pituitary gland detects GnRH, it releases FSH and LH.
Post pituitary gland release oxytocin and vasopressin
puberty onset in males
FSH and LH reach teh testis and trigger the release of testosterone.
Testosterone feeds back and binds to receptros in the pituitary gland and hypothalamus which lowers the production of GnRH, FSH and LH - keeping testosterone at a steady level
FSH in males
sperm prodcution
LH in males
testosterone production
FSH and LH in females
FSH - causes follicles to ripen
LH - induce ovulation
the menstrual cycle
When period stops:
Peak of FSH
- ovaries detect this and start follicles growing
- estradial is then produced
- when estradial is high enough it triggers the release of LH and FSH
- LH triggers ovulation
- Corpus lutem releases progesterone and more estradial to line the overian wall incase egg implants
- if no implantation - progesteron and estradial goes down again and cycle starts again
mullerian duct
embryonic structure that develops into female reproductive tract (vagina)
turner syndrome
X-containing gamete fuses with one without sex chromosome: XO (45,X)
- only monosomy that is not lethal in early development
- still 90% lethality
- female internal and external genitalia but ovaries are rudimentary
- short stature (short person, height)
pseudo-autosomal region
PAR1, PAR2
- stretches of DNA that are the same on X and Y
- SHOX is a gene in the pseudo-autosomal region which contributes to height - if haploid, short stature. If three copies you are taller
Klinefelter syndrome
- XX or XY-containing gametes fuse with a Y or X-containing gamete: XXY (47, XXY sometimes 48,XXXY)
- 1:200 life births
- male internal and external genitalia but small testes
- tall
- typically identify as men
- some female secondary sexual characteristics (breast development, less chest hair)
46, XX males
SRY gene has moved from Y to X chromosome
- phenotype varies from male to ambiguous both externally and internally
- typically identify as male
hormone based variation: androgen insensitivity syndrome
- gonads develop as testes
- androgen receptors dont work
- testosteron does not do its normal job
- 46, XY individuals develop anatomically female but without internal female genitalia
- puberty is normally late and typically identify as female
5a(alpha) reductase deficiency
5a-reductase turns testosterone into DHT
- DHT is crucial for prenatal external male genitalia
- 46XY individuals are born with female external genitalia but male internal
- at puberty, the high levels of testosterone can ‘mimic’ DHT
- they develop male genitalia after puberty
congenital adrenal hypperplasia
46,XX individuals there is high levels of testosterone because there is no 21-hydroxylase to make cortisol to feed back to the hypothalamus to stop making CRH, meaning more anrogens are being made.
- to treat this you replace the cortisol with exogenous hydrocortisone
- when young and untreated they will have a clit that looks like a penis
- 5% of CAH girls assigned female at birth have gender dysphoria
- 12% of CAH ‘girls’ assigned male at birth have gender dysphoria
21-hydroxylase deficiency
cannot make cortisol
sex differentiation in the brain: toy preferences
CAH 46,XX individuals have more masculine toy preferences
sex differences in the brain: behavioural differences
men tend to be faster in spatial mental rotation tasks
- CAH 46, XX perform better than non CAH 46,XX individuals
sex differences in the brain: structural differences
- male brains are 10% larger
- female cortex is thicker
- males have larger white matter volume & subcortical structures
- CAIS 46, XY individuals have some features that are male and some that are female
- sex differences in the brain are complex and due to many different factors.
gynophile
attracted to females
- higher T levels in embryonic development more likely to be gynophilic
androphile
attracted to males
- SCN slightly larger
- INAH-3 smaller
- anterior commisure larger
origins of sex differences in brain and behvaiour
- cultural effects
- activational hormonal effects
- organizational hormonal effects
- genetic effects
environmental effects on sex differences
- influences on brain development
- effects of practice (eg. u are better at what u spend more time doing)
- social effects (stereotypes etc)
- HOWEVER, little to NO evidence that this effects sexual orientationn
sex orientation in males
- 8% of male sheep interested in male sheep
- sexual dimorphic nucleus (SDN) of preoptic area is smaller in these males
- size of SDN is influenced by T levels.
evidence for organisational role of hormones
- correlations with measured prenatal hormones
- correlations with adult correlates of prenatal hormones
- conditions with varying prenatal hormone levels:
CAH
Androgen insensitivity syndrome
cognitive performance
- verbal abilities are better in androphile men than gynophile men
- visio-spatial performance is worse in androphile men than gynophile men
- mental rotation is faster in gynophile women than in androphile women
2D/4D ratios
- early testosterone dependent
- index and ring finger
- butch lesbians have more masculine 2D/4D
- not consistent finding in androphile men
oto-acoustic emissions
- when stimulated with a click ear makes a sound back
- louder and more frequent in women
- Gynophile women’s OAE’s closer to gynophile mens than androphile womens
ways to uncover genetic effects on sex differences
- twin studies
- genetic mappings
- concerns from an evolutionary angle
- fraternal birth order effect
twin studies
- higher concordance in monozygotic than dizygotic
- estimates from 30-100% that are gay
- possible higher concordance for women than men
genetic mapping
- androphilic men have androphillic meternal uncles
- suggests an X-chromosome inherritance pattern
- a region of the X-chromosome has been identified as related to sexual orientation
- regions on other chromosomes have been identified as well
possible mechanisms for maintaining such genes: (if gay or something maybe idk)
- heterozygote advantage
- different effects in males vs females
- kin selection
fraternal birth order effect
if you have more older brothers (biological) you are more likely to be an androphilic male
- can be explained by the maternal immunisation hypothesis, which is when if a mother has had say three sons previously, she will have ‘male’ proteins in her bloodstream
