- Slides: 14
Sex determinants Dr. Sanjaya Adikari Dept. of Anatomy
Objectives • Explain the role of sex chromosomes in sex determination • Highlight the role of Y chromosome in fetal sex determination
Female XX chromosomal sex Male XY cell gonadal sex Ovaries Testicles gonads Labia majora & minora external genitalia vulva, vagina Penis, scrotum assigned sex Breasts dress general appearance Facial hair dress
Chromosomal sex • Determined at the time of fertilization • 46, XX • 46, XY female • What determines the sex? – Presence of two ‘X’ chromosomes? – Presence/absence of ‘Y’ chromosome?
Individuals resulting from non-disjunction of sex chromosomes Karyotype Disease state Sex 46, XX normal female 46, XY normal male 45, XO Turner’s syn female 47, XXY Klinefelter’s syn male
XY XX nondisjunction X Y XX O XXX XXY XO OY Turner’s syn lethal Super females Klinefelter’s syn Can one get XYY?
Live with ‘X’ & Sex with ‘Y’
External genitalia indifferent stage female
XY Role played by hormones XX testicles ovaries androgens oestrogen male external genitalia female external genitalia male secondary sex characteristics female secondary sex characteristics
Determining the number of X and Y Sex chromatin Barr body for X F body for Y
Barr body • Condensed inactive ‘X’ in interphase nuclei • Near the nuclear membrane • All ‘X’ in addition to one ‘X’ become BB’s Barr body
F body • Fluorescence stained ‘Y’ • This ‘Y’ is active F body
One BB No FB ? ? XX One BB One FB XXY No BB No FB XO No BB Two FB XYY
References • http: //www. people. virginia. edu/~rjh 9 u/sexdet. html • http: //www. dushkin. com/connectext/psy/ch 10/biodet. mhtml • http: //www. aaa. dk/TURNER/ENGELSK/XYY. HTM#name • Review of medical physiology by William F. Ganong • Medical embryology by Jan Langman