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Sex determinants Dr. Sanjaya Adikari Dept. of Anatomy.

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Presentation on theme: "Sex determinants Dr. Sanjaya Adikari Dept. of Anatomy."— Presentation transcript:

1 Sex determinants Dr. Sanjaya Adikari Dept. of Anatomy

2 Objectives Explain the role of sex chromosomes in sex determination Highlight the role of Y chromosome in fetal sex determination

3 Objectives ?? Different ways of defining the sex/gender Influence by maternal hormones on the fetal sex Simple laboratory methods to count the number of ‘X’ and ‘Y’ chromosomes Examples of diseases resulting from altered number of sex chromosomes

4 Female Male cell gonads external genitalia general appearance XX XY OvariesTesticles Labia majora & minora vulva, vagina Penis, scrotum Breasts dress Facial hair dress chromosomal sex gonadal sex assigned sex

5 Chromosomal sex Determined at the time of fertilization 46, XXfemale 46, XYmale What determines the sex? –Presence of two ‘X’ chromosomes? –Presence/absence of ‘Y’ chromosome?

6 Individuals resulting from non-disjunction of sex chromosomes KaryotypeDisease stateSex 46, XXnormalfemale 46, XYnormalmale 45, XOTurner’s synfemale 47, XXYKlinefelter’s synmale

7 XY X Y XX O XXXXXYOYXO Can one get XYY? Super femalesKlinefelter’s synTurner’s synlethal nondisjunction

8 Live with ‘X’ & Sex with ‘Y’

9 male female External genitalia indifferent stage

10 XY testicles androgens male external genitalia male secondary sex characteristics XX ovaries oestrogen female external genitalia female secondary sex characteristics Role played by hormones

11 Sex chromatin F body for Y Barr body for X Determining the number of X and Y

12 Barr body Condensed inactive ‘X’ in interphase nuclei Near the nuclear membrane All ‘X’ in addition to one ‘X’ become BB’s Barr body

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

14 ?? One BB No FB One BB One FB No BB No FB No BB Two FB XX XXY XO XYY

15 References http://www.people.virginia.edu/~rjh9u/sexdet.html http://www.dushkin.com/connectext/psy/ch10/biodet.mhtml http://www.aaa.dk/TURNER/ENGELSK/XYY.HTM#name Review of medical physiology by William F. Ganong Medical embryology by Jan Langman


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