Sex-Linked TraitsSex-Linked TraitsCh. 10.5Ch. 10.5

Sex-Linked GenesSex-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 Offspring sex depends on whether

the sperm cell that fertilizes the egg the sperm cell that fertilizes the egg carries an X or a Y carries an X or a Y

Sex-linked geneSex-linked gene = any gene that is = any gene that is located on a sex chromosome (most located on a sex chromosome (most found on the X chromosome) found on the X chromosome)

Discovery of Sex-Linked Discovery of Sex-Linked GenesGenes

Thomas MorganThomas Morgan discovered sex-linked discovered sex-linked genes while studying genes while studying eye color in fruit flies eye color in fruit flies

White eyes are rare in White eyes are rare in fruit flies (most have fruit flies (most have red eyes) red eyes)

White Eye Color White Eye Color Inheritance in Inheritance in DrosophilaDrosophila

Summary: P: XRXR x XrYF1: 2XRXr, 2XRY F2: XRXR, XRXr, XRY, XrY

Conclusion: The gene involved in eye color is on the X chromosome!

Color blindness, mostly in malesColor blindness, mostly in males color blindness testcolor blindness test FYI:FYI:

– Achromatopsia - complete Achromatopsia - complete color blindnesscolor blindness, , seeing only shades of gray seeing only shades of gray

– Deuteranopia - difficulty telling the Deuteranopia - difficulty telling the difference between red/purple and difference between red/purple and green/purple green/purple

– Protanopia - difficulty telling the difference Protanopia - difficulty telling the difference between blue/green and red/green between blue/green and red/green

– Tritanopia - difficulty telling the difference Tritanopia - difficulty telling the difference between yellow/green and blue/green) between yellow/green and blue/green)

Sex-Linked DisordersSex-Linked Disorders

Sex-Linked Disorders Sex-Linked Disorders Continued…Continued…

Hemophilia, (blood Hemophilia, (blood fails to clot) fails to clot)

Much more Much more common in males!common in males!