Sex Determination and Sexual Differentiation Flashcards
what three levels do differences between males and females exist
genetic sex
gonadal sex
phenotypic sex
when is genetic sex determined
what determines it
at time of fertilization
depends on if the sex chromosome contained in the fertilising sperm
what determines gonadal sex
genetic sex
presence of absence of Y c’some
what are the features of a sexually undifferentiated foetus reproductive organs
both male and female internal ducts present (Wolffian and Mullerian ducts)
cloaca (forms external genitalia)
bipotential gonadal ridge (forms gonads)
what is the SRY gene
what does it encode
Sex-determining Region of Y c’some t
encodes testes determining factor
what is the role of TDF
acts as a transcription factor for testicular differentiation genes e.g.
MIF and androgen receptors
what determines phenotypic/anatomic sex
gonadal sex
why does the removal of gonads from either sex foetuses result in a female adult
sexual characteristics of other tissues are determined by the gonads not the chromosomes in the tissues
what is the Mullerian duct
foetal internal duct that differentiates to become internal female genitalia
what is the Wolffian duct
foetal internal duct that differentiates to become internal male genitalia
pathway leading to Mullerian duct regression
male SRY gene -> TDF -> testis containing Sertoli cells -> MIF -> Mullerian duct regression
pathway leading to Wolffian duct development
male SRY gene -> TDF -> testis containing Leydig cells -> Testosterone -> Wolffian duct development
pathway leading to Mullerian duct development
no male SRY gene -> no TDF -> ovary -> no MIF inhibition -> Mullerian duct development
pathway leading to Wolffian duct regression
no male SRY gene -> no TDF -> ovary -> no Testosterone stimulation -> Wolffian duct regression
XY early castrate
no T
no MIF
Mullerian ducts develop
XX early castrate
no T
no MIF
Mullerian ducts develop
XY unilateral early castrate
Untreated side has normal development
treated side no T and no MIF so Mullerian ducts develops
XY early castrate treated with T
T
no MIF
Wolffian duct develops
Mullerian duct not inhibited and also develops
XX treated with T
T
no MIF
Wolffian duct develops
Mullerian duct not inhibited and also develops
what hormone controls development of external genitalia
how is it synthesised
DHT
Testosterone - 5α-reductase -> dihydrotestosterone
what causes male phenotypic sex
DHT causes cloaca to develop male
what causes female phenotypic sex
no T so no DHT so cloaca reverts to female
what happens in OY and OX aneuploidies
OY - lethal cannot be born
OX - female with Turner’s syndrome
Turner’s syndrome symptoms
non-functional ovaries - absence of menstrual cycle
sterility
short stature
webbed neck ?!
webbed feet
what is a true hermaphrodite
gonadal tissue and germ cells must be present (how is that possible if they come from the same thing? one of each?)
what is a male pseudohermaphrodite
what causes it
only testicular tissue but with some female morphological features
failure of synthesis or action of hormones
what is a female pseudohermaphrodite
what causes to
only ovarian tissue but with some male morphological features
inappropriate synthesis/exposure to androgens
what is 21-hydroxylase
what happens in deficiency
enzyme involved in aldosterone and cholesterol synthesis
deficiency results in genetic females with male features, disrupted or lack of menstruation and ambiguous genitalia (?!)
