2.  Recall that the 23 rd chromosome in humans dictates the gender of the individual  The Y chromosome is much smaller, and carries much less genetic info

3. X chromosome Y chromosome Colourblindness Hemophilia 900-1600 genes 70-200 genes

5.  Genes found on the either chromosome are called sex-linked traits  Far more are found on the X, and not found on the Y  What does this mean for males??  They are more susceptible to conditions found on the Y chromosome  All X-linked conditions are expressed more so in males

6.  Can result from a defect in one of three genes found on X chromosome

8.  Possible Inheritance of Colorblindness Allele

9. Hemophilia  Genes for clotting found on X chromosome  Defects lead to deficiencies in expression of coagulation factors  Patients blood does not clot as easily ◦ Cuts can be fatal

11. Duchenne Muscular Dystrophy  Another X-linked condition  Sufferers lack a muscle protein, skeletal muscle degrades

12.  One of the X chromosomes is inactivated in females (randomly)  Chromosome forms a dense region that attaches to nuclear envelope  Stains darker, visible under light microscope  Called a Barr Body  Discovered by a Canadian cytogeneticist Dr Murray L. Barr

13. Other dark spots are nucleoli

16.  Used in 1966 Olympics to test for males attempting to pass as females  Resulted in the stripping of medals from individuals because of ambiguous genital sex ◦ Genetic defect that allows males to appear as females  Also successfully indentified a number of cases of testicular feminization syndrome (androgen insensitivity syndrome) ◦ Error in androgen receptors resulting in XY individual developing phenotypically as females