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Sex-linked Inheritance

Sex-linked Inheritance. Objectives. Know the difference between autosomal chromosomes and sex chromosomes. Understand sex-linked inheritance. Be able to create a family pedigree. Solve sex-linked problems using a Punnett square. Gender Determination in Humans.

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Sex-linked Inheritance

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  1. Sex-linked Inheritance

  2. Objectives • Know the difference between autosomal chromosomes and sex chromosomes. • Understand sex-linked inheritance. • Be able to create a family pedigree. • Solve sex-linked problems using a Punnett square

  3. Gender Determinationin Humans • Humans have 23 pairs of chromosomes. • 22 of them are called autosomal. • The 23rd pair are the sex chromosomes. • The sex chromosomes determine whether an offspring will be male or female. • XX = Female • XY = Male

  4. Pedigree Marriage XY XX Mother Father Children XY XY XX Son Daughter Son Oldest Youngest

  5. X X X X X C C c c c X C Red/Green Colorblindness • The gene which allows us to distinguish between red and green is on the X chromosome. = Female with normal vision = Female carrier = Female who is colorblind

  6. Y X X Y C c Red/Green Colorblindness • For males, it appears to be easier to inherit sex-linked traits. = Male with normal vision = Male who is colorblind

  7. XY XX c C C Pedigree Mother Father ?? ?? ?? Son Daughter Son

  8. XY XY XX C C C c Pedigree XY XX c C C Mother Father Son Daughter Son

  9. X X X Y X Y Y XY c c c c c X X X X C C C c X c Using a Punnett Square XX C c

  10. Y Y XY Y X X X X c c c c c X X X X C C C c X c Genotype & Phenotype XX C c Female Carrier Female Colorblind Male Normal Male Colorblind

  11. Hemophilia A sex-linked bleeding disorder (dangerous) XX = Female normal H H XX = Female carrier H h XX = Female with hemophilia h h XY = Male normal H XY = Male with hemophilia h

  12. Review • What is the general format for a pedigree? • Why are Punnett Squares better to use sometimes? • Why do sex-linked traits affect males more frequently than females?

  13. Important Point • Some sex-linked traits are dominant. This means that even if the female is only a carrier of the illness, she will be affected with the disease. • The dominant gene dominates the gene pair.

  14. Practice Problems • Muscular dystrophy is a sex-linked illness. Draw a pedigree showing the sons and daughter of an affected father and a normal mother. • Draw a Punnett Square to show the same illness for an affected father and a carrier mother.

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