Sex differences

Chromosomes

Made of DNA and protein. Genetics. Female = XX

Male = XY

Testis determining factor

Gene SRY located on Y chromosome, turns fetal gonad into testis. In its absence, gonad becomes ovary

Anti-mullerian hormone

de-feminising hormone produced by early testis

Androgens

Masculating hormone produced by early testis

Summary of male sex determination

Testis determining factor turns primordial gonads into testis.

Mullarian goes due to anti mullerian hormones

Androgens cause wolfram system to develop, developing external genitalia develops

summary of female sex determination

Primordial develops into ovaries, no hormones needed. Mullarian system turns into internal genitalia. Wolfian system withers without androgens.

organisational hormones

Effect remains after hormone has been removed. Often occurs during sensitive period.

Eg wider pelvis in women, and wide shoulders/lower voice in men

Activation hormones

Effect is reversible, depending on presence or absence of hormone.

Eg increased facial hair/muscle mass in men, and increased breast development in women

Gondatopins

Release hormone of GnRH which starts off puberty. Which then signals FSH and LH

FSH

Male = sperm production

Female = follicles ripen

LH

Male LH = testosterone production

Female LH = induce ovulation

Hypothalami-pituitary-gonadal axis

Hypothalamus releases GnRH. GnRH signals pituitary gland to release FSH and LH. FSH and LH act on gonads stimulating production of sex hormones eg development of egg and sperm

Menstrual cycle

HPG axis. Follicles ripen due to FSH. Follicle produces estrodoil. This triggers FSH and LH to release ovulation. Ruptured follicle develops into corpus luteum, begins to release progesterone which prepares lining of uterus.

While ovum goes through fallopian tube due to rowing action of cilliated cells. If not fertilised, progesterone and estradoil levels fall and cycle begins

Androgen insensitivity syndrome

Gonads develop as testes. Androgen receptors don’t work so testosterone can’t do its normal job. Develop anatomically as a female, but without I real female genitalia. Puberty typically late. Typically identify as women

5a reductase defiency

Can’t convert testosterone into DHT, but at puberty the high levels of testosterone can mimic DHT. Develop male genitalia (guevedoces). After puberty, mostly identify as men

Congenital adrenal hyperplasia

High levels of prenatal testosterone in girls. Ambiguous external genitalia in girls. Some assigned male at birth. 5% of assigned females have gender dysphoria, whereas 12% of assigned male

Sex behavioural differences

toy preference, play style and prenatal testosterone.

Men faster in mental rotation tasks so is CAH. Suggesting role of testosterone

Sex structural differences

Male brains 10% larger. Female cortex thicker (more grey matter). Males larger white matter volume and subcortical structures (hypothalamus, amygdala etc)

Environmental effects on sexual orientation

Exposed in childhood, social effects (stereotypes). However little evidence this affects sexual orientation

Activation hormonal effects on sexuality

Testosterone levels, estradoil levels, menstrual cycle. However found it effects sexual motivation not orientation

Organisational hormones on sexuality

Prenatal hormones (testosterone). Cognitive performance = gay better at verbal but worse at spatial (male). Female gay better at mental rotation. Butch lesbians have more masculine 2D/4D.

Ota-acoustic emissions (when click, ears make sound back). Gay women closer to straight males.

CAH females more likely to be gay

Genetic effects on sexuality

Higher concordance in mz than dz twins

Gay men often have gay uncles in mother’s side suggesting X chromosome inheritance.

Evolutionary concerns = offspring

Fraternal birth order effect

The odds of having a gay son increases with the amount of sons you’ve had as a mother. So man is more likely to be gay if they gave more older brothers from the same mother

Maternal immune hypothesis

Mother’s immune response to protein neuroligin 4 Y-linked predicted probability of having gay son

Trans male genetic predisposition

Long version of estrogen receptor beta and adonosene version of estrogen receptor alpha

Genetic predisposition of trans female

Long version of androgen receptor and short version of estrogen receptor beta + alpha

Pre-transition brain differences

Brain volumes in line with natal sex.

MtF show more feminine cortical thickness.

FtM show more masculine basal ganglia and white matter tracts

Androstenedione

Can be converted into testosterone or estrogen for secondary sexual characteristics

gonad

Organ that produces gametes (reproductive cells) and hormones. Testes and ovaries

Preoptic area of hypothalamus

Regulates sexual behaviour and reproductive functions. Regulates GnRH

Kisspeptin

Peptide hormone that regulates puberty and reproductive function. Produced in hypothalamus

Vasapressin

Hormone produced in hypothalamus and released in pituitary gland, influences sexual behaviour

INAH3

Sexual brain region in hypothalamus, smaller in homosexual men

Anterior commissure

Fibres that connects two brain areas. Larger in women do better at verbal processing and emotional response

What determines a baby’s chromosomal sex

Presence or absence of Y chromosome

Persistent Müllerian duct syndrome

Individual has male external genitalia with testes.

Male and female internal genitalia

Consequences on the HPG axis of taking anabolic steroids

testes make low amounts of testosterone, the hypothalamus produces less GnRH, testes will shrink

Complete androgen insensitivity syndrome women

Leads to lack of pubic hair

what does anti-androgen drugs do to men?

Make a man uninterested in sex

What would you need to investigate to distinguish an activational from organisational effect of hormone treatment in transgender people?

Explain activation and organisation

Time of hormone treatment, if in adulthood more likely to be activational

Persistence after stopping hormones

Exposure history

Functional (activation) vs structural (organisational)

Longitudinal studies - tracks changes over time