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Sex Linkage

Sex Linkage. X-linked Traits. 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. X chromosome. Y chromosome. Colourblindness. Hemophilia. 70-200 genes. 900-1600 genes.

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Sex Linkage

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  1. Sex Linkage

  2. X-linked Traits • Recall that the 23rd 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 70-200 genes 900-1600 genes

  4. 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

  5. Colourblindness • Can result from a defect in one of three genes found on X chromosome

  6. Possible Inheritance of Colorblindness Allele

  7. Other Conditions 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

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

  9. X Chromosome Inactivation • 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

  10. Other dark spots are nucleoli

  11. 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

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