Sex determinants Dr Sanjaya Adikari Dept of Anatomy

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Sex determinants Dr. Sanjaya Adikari Dept. of Anatomy

Sex determinants Dr. Sanjaya Adikari Dept. of Anatomy

Objectives • Explain the role of sex chromosomes in sex determination • Highlight the

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

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,

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

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

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’

Live with ‘X’ & Sex with ‘Y’

External genitalia indifferent stage female

External genitalia indifferent stage female

XY Role played by hormones XX testicles ovaries androgens oestrogen male external genitalia 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

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

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

F body • Fluorescence stained ‘Y’ • This ‘Y’ is active F body

One BB No FB ? ? XX One BB One FB XXY No BB

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.

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