1. Sex linked Inheritance

2. Sex determination
Sex determination in fruit flies (where it was discovered)
Females have 2 X chromosomes
Male shave one X and one Y chromosome
Segregation of the sex chromosomes occurs in meiosis
Morgan’s famous fruit fly experiment to demonstrate sex linked inheritance

3. Sex linked genes in humans
Because males have 1 X chromosome any X – linked gene is expressed, recessive or not.
Males pass the X chromosome onto their daughters so sex linked genes pass from father to daughter and may be expressed in the sons of those daughters.

4. Sex linked genes in humans
Colorblindness
Dominant allele is normal color vision
Recessive allele causes colorblindness
10% of males are colorblind
Hemophilia
Blood clotting protein coded for on the X chromosome
Duchenne Muscular Dystrophy
Protein called dystrophin is missing, causes muscles to break down, candidate for gene therapy