Presentation on theme: "Urogenital Development II & Sex Determination"— Presentation transcript:
1 Urogenital Development II & Sex Determination 2-6-03Urogenital Development II& Sex DeterminationGreg DresslerAssoc. ProfessorDept. of Pathologyx46490
2 Gross morphological differences between sexes are Not observed until about the 7th week of gestation.This early period from 0-7 weeks is called the indifferentstage.However, differences at the genetic and microscopic levels are alreadyApparent.Female nuclei contain a Barr body, which is an inactivated X chromosomeMale embryos show gene expression of some Y specific proteins such asSRY, testis determining factor, and the H-Y antigen, a minor histo-compatibility antigen.
3 Sex determination begins at fertilization Humans have 46 chromosomes-22 pairs of autosomes- 2 sex chromosomesIn general: females are - 46, XXmales are , XY
4 In mammals, the presence of a Y chromosome determines the male phenotype.
6 Evidence that SRY is the testis determining factor SRY is detected in gender reversal:XX males who have a translocation of the sry region toan X or another chromosomeXY females who have a deletion of the SRY regionIn transgenic mice, a 14 kb genomic DNA encoding SRY cantransform XX females into phenotypic males.SRY is expressed in male gonads at the time of sex determination.SRY encodes a DNA binding protein of the HMG class and is thoughtto function as a master switch for the regulation of testis specificgenes.
7 Migration of primordial germ cells from theposterior extra-embryonic mesodermthrough the mesenteriesand into the gonadal ridge
28 Genetic abnormalities of sex determination Turner’s syndrome - gonadal dysgenesis45,X0 genotype results in degeneration of the promordial germ cellsafter reaching the gonadal ridge. Gonads fail to differentiate anddo not secrete androgens. External genitalia is female but remainsinfantile.True Hermaphroditism- generally 46,XX and appear female but haveovotestis, with both spermatagonia and ovarian follicles (veryrare and usually raised as female).Pseudohermaphrodidism- Males are usually 46,XY with insufficient hormoneproduction, phallic hypoplasia, and remnants of the paramesonephricduct present. Femaler are usually 46,XX but produce too muchandrogenic hormones by the adrenal cortex and exhibit masculinizationof external genitalia.Testicular Feminization- genetically male, 46XY, but phenotypically female.Individuals have internal testis, produce testosterone but areinsensistive to androgens due to a receptor mutation.