Role of chromosomes and hormones in biological sex development

Role of chromosomes in bio sex

chromosomes made of dna
genes = short sections of dna → influence physical/psychological traits
bio sex = determined by sex chromosomes
female = XX
male = XY
female parent provides one X
male parent provides either X or Y
Y chromsome contains SRY gene → testes development in XY embryo

role of hormones in bio sex

chromosomes influence production of sex related hormones
hormones influence sex related development
before birth - hormones → development of reproductive organs (testes, penis, ovaries, vagina)
act upon brain development
testosterone: 10x higher in males typically. controls development of male sex organs pre-birth (end of 2nd month of preg)
oestrogen: levels much higher in females. promotes development of endocrine system pre-birth. puberty - secondary sexual characteristics (e.g. breast growth, widen hips, menstrual cycle). males - oestrogen affects develop of male sex organs, erectile function & process of sperm cell production.
oxytocin: XX females produce more frequently than males. during & after childbirth particularly. stimulates lactation.

STRENGTH: testosterone

role of testosterone in sex development supported by evidencee
link confirmed by Wang et al 2000.
male hypogonadism - testes produce insufficient levels of testosterone
Wang gave 227 hypogonadal adult males test therapy for 180 days - changes in body shape, muscle strength, sexual function monitored
testosterone replacememnt improved sexual function, libido & mood - significant increases in muscle strength
powerful and direct influence on male physical develp - even in adulthood

LIMITATION: counterpoint

complete androgen insensitivity syndrome (CAIS)
presence of testosterone on its own doesn’t determine bio sex
people with CAIS = genetically male XY & produce typical/high amounts of testosterone
body unable to respond to it
female external genitalia & appear female
testosterone alone = not enough for male development
other bio factors shape sex

LIMITATION: SRY gene

evidence doesnt always show XY chromosomes leading to male dev
Wu et al 2012: ‘knockout experiments’ in mice → removing SRY gene in CXY embryos → development of ovaries and no testes
SRY gene importance seen in humans → Swyer syndrome (XY chromosomes, nonfunctional/deleted SRY gene) - Coutin et al 1996: develop as females; non-functional female gonads
XY chromosomes not only determinant of male dev

LIMITATION: environmental influence

Bull (1987): reptiles - temp of eggs determine whether embryos develop as male/female even if individual’s genes are the same
Muerkoster et al 2020: mrecent study - prenatal exposure to phthalates (chem in plastics that affect endocrine func) affect sex development (e.g. - e.g. cause reduced testosterone) - affect fertility later in life
chromosomes & hormones arent only influences