Ontogenesis of sex in mammals

Ontogenetic notes

 * Gonosomal complement
 * female:XX,
 * male: XY.


 * The Y chromosome (short arms) contains a highly conserved SRY (sex determining region of Y)' region, which contains the 'testis specific protein Y-linked (TSPY) gene for male gonadal differentiation'.
 * Gene TSPY is peculiar in that it contains no introns and ends with a polyadenyl-like sequence (hypothesized to have originated by reverse transcription from mRNA, but this must have happened a very long time ago - 166 million years).
 * The SRY region is homologous to genes for the formation of non-histone proteins on the X chromosome.


 * The product of the TSPY gene binds to the promoter:'
 * the gene for cytochrome-P450-aromatase, which converts testosterone into the female hormone estradiol and inhibits its transcription,
 * the Müllerian inhibitory substance gene, which is responsible for testicular differentiation and female organ regression and activates its transcription.


 * By week 6, human gonadal development is indifferent,
 * the bases of the gonads develop in the plica genitalis,
 * male:''
 * the testes develop from the coelomic epithelium,
 * Sertoli's bb' - from the ductal cells of the mesonephros, producing MIF (Müllerian inhibition factor),
 * Leydig's bb' - from the mesenchyme, under the action of hCG they start to produce testosterone, which stimulates the development of Wolffian ducts and male external genitalia and the descent of the testes,
 * sperm development is regulated by genes on the long arms of the Y chromosome,
 * female:''
 * in the absence of SRY, the fallopian tubes, uterus and part of the vagina develop from the Müllerian ducts,
 * female genitalia develop under the influence of estradiol,
 * the coelomic epithelium gives rise to the ovarian cortex,
 * oogonia enter mitotic division 3 to 6 months prenatally, forming oocytes,
 * indeferent bb change to follicular (ca. 4th month), surround the oocyte and give rise to primordial follicles → oocytes of primordial follicles enter reductive division and remain in the dictyotenic stage (diplotene prophase of meiosis I) until follicle maturation at puberty (and beyond),
 * development of sexual dimorphism is completed at 12 to 14 weeks' pregnancy''.

Gonadal dysgenesis

 * Turner syndrome - karyotype 45,X.

True hermaphroditism

 * Basis of both ovary and testes,
 * chimera 46,XX/46,XY (fusion of two zygotes).

Male pseudohermaphroditism

 * Testes and female or bilateral genitalia,
 * testicular feminization' - insensitivity to testosterone, no receptors for it are expressed, karyotype 46,XY,
 * incomplete insensitivity to testosterone,
 * mutations geneu for 5α-reductase,
 * mosaicism 45,X/46,XY.

Female pseudohermaphroditism

 * ovaries, 'masculinization of the external genitalia
 * overproduction of testosterone in the adrenal glands
 * 21-hydroxylase block (adrenogenital syndrome, AR, gene located in the HLA class III region)

Related Articles

 * Chromosomal sex determination