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