Sex Linkage
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Transcript of Sex Linkage
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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
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X chromosome
Y chromosome
Colourblindness
Hemophilia
900-1600 genes
70-200 genes
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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
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Can result from a defect in one of three genes found on X chromosome
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Possible Inheritance of Colorblindness Allele
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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
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Duchenne Muscular Dystrophy Another X-linked condition Sufferers lack a muscle protein, skeletal
muscle degrades
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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
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Other dark spots are nucleoli
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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