Sex-Linked Traits Ch. 10.5

Sex-Linked Genes Sex chromosomes: X and Y Sex chromosomes: X and Y (male: XY, female: XX) (male: XY, female: XX) Offspring sex depends on whether the sperm cell that fertilizes the egg carries an X or a Y Offspring sex depends on whether the sperm cell that fertilizes the egg carries an X or a Y Sex-linked gene = any gene that is located on a sex chromosome (most found on the X chromosome) Sex-linked gene = any gene that is located on a sex chromosome (most found on the X chromosome)

Discovery of Sex-Linked Genes Thomas Morgan discovered sex-linked genes while studying eye color in fruit flies Thomas Morgan discovered sex-linked genes while studying eye color in fruit flies White eyes are rare in fruit flies (most have red eyes) White eyes are rare in fruit flies (most have red eyes)

White Eye Color Inheritance in Drosophila Summary: P: X R X R x X r Y F1: 2X R X r, 2X R Y F2: X R X R, X R X r, X R Y, X r Y Conclusion: The gene involved in eye color is on the X chromosome!

Color blindness, mostly in males Color blindness, mostly in males color blindness test color blindness test color blindness test color blindness test FYI: FYI: –Achromatopsia - complete color blindness, seeing only shades of gray color blindnesscolor blindness –Deuteranopia - difficulty telling the difference between red/purple and green/purple –Protanopia - difficulty telling the difference between blue/green and red/green –Tritanopia - difficulty telling the difference between yellow/green and blue/green) Sex-Linked Disorders

Sex-Linked Disorders Continued… Hemophilia, (blood fails to clot) Hemophilia, (blood fails to clot) Much more common in males! Much more common in males!