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Sex-Linked Traits

Sex-Linked Traits. The genetics of genes located on the sex chromosomes. Objective. I will be able to predict the probable outcome of a genetic cross for sex-linked traits by using and analyzing Punnett squares. Review: Autosomal Punnett Squares.

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Sex-Linked Traits

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  1. Sex-Linked Traits The genetics of genes located on the sex chromosomes

  2. Objective • I will be able to predict the probable outcome of a genetic cross for sex-linked traits by using and analyzing Punnett squares.

  3. Review:Autosomal Punnett Squares • Red roses (R) are dominant over yellow roses (r). • Make a Punnett square for a heterozygous red rose crossed with a yellow rose. • What are the possible phenotypes of the offspring? R r Rr rr r r rr Rr R = red r = yellow

  4. Review:Sex Determination • Sex is determined by the sex chromosomes • Male: XY • Female: XX

  5. What are sex-linked genes? Blood clotting • Sex-linked genes: genes that are located on the sex chromosomes • X chromosome has genes that affect many traits • Y chromosome has few genes • Wimpy Y!!!  eyesight estrogen muscle protein

  6. How do we write sex-linked traits? • Dominant, recessive rules still apply, but alleles are written like exponents on the X • Y does NOT have any alleles! Example: • In fruit flies eye color is sex-linked. Red (R) eyes is dominant over white eyes (r) • female = XRXR or XRXr • males = XRYor XrY

  7. EXAMPLES: Colorblindness • The inability to see distinct colors. • XB = normal vision • Xb = colorblind Practice: What is the phenotype for these individuals? 1. XbY: 2. XBXb:

  8. Hemophilia • Hemophilia is a sex-linked recessive trait defined by the absence of blood clotting factors. • These proteins slow and stop bleeding. • XH = no hemophilia • Xh = hemophilia Practice: 3. Write the genotype of a male that has hemophilia.

  9. Duchenne Muscular Dystrophy (MD) • Missing a key muscle protein, which causes progressive weakening of the muscles and a loss of coordination • Lifespan: early 20s • XM = no MD • Xm = has MD Practice: 4. Write the genotype of a female that is normal but carries (is heterozygous) for MD.

  10. When it comes to sex-linked disorders, males are unlucky! Why?!

  11. Males are more likely to have sex-linked disorders • If a male inherits one “bad” copy of the gene he will express the disorder • Example: XrY • Females need to inherit two “bad” copies in order to express the disorder • Example: XrXr

  12. Autosomal vs. Sex-Linked Review Y Y Xb XB XB Male Female

  13. Sex-linked Punnett Squares Practice Eye color in Drosophila flies is sex linked! A heterozygous female with red eyes is bred with a male with white eyes. Practice: 5. Complete a Punnett square to show this cross! 6. What is the phenotype of the offspring?

  14. Practice #7 In cats, allele L codes for long fur and allele l produces short fur. The alleles for fur are located on the X-chromosome. Complete the following cross: Does the mom cat have short or long hair? Long XL XL XLY What is the probability that a MALE kitten will have short hair? 50% XL Xl XlY What is the probability that a female kitten will have short hair? 0%

  15. Practice #8 Color blindness is a sex-linked recessive trait. If a male with color blindness and a female that is acarrier(heterozygous) for color blindness have kids, what is the probability that their child will be color blind? Xb Y XB = normal vision Xb= color blindness XB XB Xb XB Y Xb Xb Y Xb Xb

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