Sex Determination and Gonadal Development chromosomal sex determination

Sex Determination and Gonadal Development

chromosomal sex determination development of gonads environmental sex determination

Chromosomal Sex Determination in Mammals

Primary sex determination of the gonads strictly chromosomal X and Y Y carries gene that encodes testis-determining factor - no default state

2 ndary sex determination of bodily phenotype related to the organism's sex does not affect the nature of the gonad hormones from gonads

Primary sex determinatio n Secondary sex determination ->

Mechanisms of mammalian primary sex determination

Male sex determinants SRY Sexdetermining Region of the Y chromosome

Association of DNA with the SRY protein cause the DNA to bend 7080 degrees. The black structure represents the HMG box of the SRY protein. The red coil is the double helix of DNA specifically bound by SRY.

indirect mechanism induces cells to secrete a chemotactic factor (g. r) -> migration of mesonephric cells into XY gonad ->gonadal epithelium = Sertoli

SOX 9 autosomal gene involved in sex determination of males encodes a transcription factor that contains HMG (high-mobility group) box found in all vertebrates

SOX 9 (continued) activates Amh gene in Sertoli cells (anti-Mullerian) activated by Sry in mammals but not in other vertebrates 1 functional allele -> campomelic dysplasia

SF 1 steroidogenic factor for the formation of bipotential gonad remains at high levels in the XY genital ridge, not in XX

masculinizes the Leydig and Sertoli cells works with SOX 9 to activate Amh in the Sertoli cells activates genes encoding enzymes that make testosterone (Lc)

Female sex determinants DAX 1 potential ovarydetermining gene on the X chromosome expressed in the genital ridge after Sry

DAX 1 (continued) antagonist to function of Sry downregulates SF 1 expression

WNT 4 on the autosome expressed in the genital ridge at it bipotential state maintained in XX gonads in the absence of Sry

Secondary sex determination

Temporal phases within embryo during organogenesis during adolescence

AMH from the Sertoli cells causes degeneration of the Müllerian duct may cause sex reversal in mammals

binds with mesenchyme around M duct -> mesenchyme secrete paracrine factor -> apoptosis of m. d. epithelium

Testosterone from fetal Leydig cells causes Wolfian duct to differentiate into epididymis vas deferens seminal vesicle

causes urogenital swellings to develop into: scrotum penis if converted into 5 dihydrotestosterone

Insulin-like hormone 3 from the Leydig cells required for the descent of the gonads into the scrotum lack in females deregulates menstrual c

Estrogen in females, causes differentiation of m. d. -> uterus oviducts cervix promotes breast dev't

in males, regulates function of vas efferens in absorbing water from rete testis (> females) -> concentrates sperm longer lifespan and greater density

Environmental sex determination

Temperature-dependent

aromatase converts testosterone to estrogen < aromatase = male > aromatase = female activity is dependent on temperature and Sox 9

Location-dependent