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Sex-Linked Punnett

Sex-Linked Punnett. Karyotype A photograph of a cell’s chromosomes arranged in pairs according to size. Normal Karyotype: 23 pairs of chromosomes. pairs 1-22 are autosomes pair 23 are sex chromosomes. 24-5. X. Y. Sex Chromosomes. X chromosome has over 1,000 genes

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Sex-Linked Punnett

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  1. Sex-Linked Punnett

  2. KaryotypeA photograph of a cell’s chromosomes arranged in pairs according to size

  3. Normal Karyotype:23 pairs of chromosomes • pairs 1-22 are autosomes • pair 23 are sex chromosomes 24-5

  4. X Y Sex Chromosomes

  5. X chromosome • has over 1,000 genes • most genes on the X chromosome do not have corresponding alleles on the Y chromosome • Y chromosome • has only a few dozen genes • some genes are unique only to the Y chromosome

  6. Sex-Linked Traits • Those traits whose genes are found on the X chromosome but NOT on the Y chromosome

  7. Examples of Sex-linked Traits: • Red-green colorblindness • Male Pattern Baldness • Hemophilia (Queen Victoria was a carrier) • Duchenne Muscular Dystrophy (fatal)

  8. Color Blindness “tests”

  9. The test below is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

  10. Females = XX –carry 2 alleles for a sex-linked trait • Males = XY – only carry 1 allele for a sex-linked trait, so it is easier for them to get sex-linked diseases

  11. Sex-Linked Traits, cont. • Males receive sex-linked traits from their mother because their mother gives them the X chromosome and their father gives them the Y chromosome

  12. Example of Sex-Linked Trait • H = Normal blood clotting • h = Hemophilia • Genotypes Phenotypes HH Normal Hh Normal/Carrier hh Hemophilia

  13. Example of Sex-Linked Trait XHY • Normal male: • Male with Hemophilia: • Normal female (not a carrier for hemophilia – homozygous): • Normal female (carrier for hemophilia – heterozygous): • Female with Hemophilia: XhY XHXH XHXh XhXh

  14. Sample Problems

  15. 1. XHXh x XHY • Chances of: • a. hemophiliac child? • b. hemophiliac son? • c. hemophiliac daughter? • d. daughter who is carrier? ¼ or 25% XHXh XH Y XHXh XHXH ½ or 50% XHY XhY 0% ½ or 50%

  16. 2. A woman who is a carrier for hemophilia marries a hemophiliac man. XHXh x XhY • Chances of: • a. hemophiliac child? • b. hemophiliac son? • c. hemophiliac daughter? XH Xh 2/4 or 50% Xh Y XhXh XHXh ½ or 50% XHY XhY ½ or 50%

  17. 3. A normal man marries a Homozygous normal woman. XHXH x XHY • Chances of: • a. Will any of their kids be hemophiliacs? XH XH XH Y XHXH XHXH XHY XHY 0/4 or 0%

  18. A normal woman (whose father is a hemophiliac) marries a hemophiliac man. • What are their genotypes? Her dad - XhY XHX? XhY XHXh and XhY

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