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Sex-Linked Inheritance

Sex-Linked Inheritance. Sex determined by genes found on the X and Y chromosome Females: egg produced with an X chromosome Males: ½ sperm cells contain X; and the other ½ contain Y There is a 50/50 chance of child being a boy/girl. Sex Determination. X X. X Y. X. X. X. X. X. Y.

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Sex-Linked Inheritance

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  1. Sex-Linked Inheritance

  2. Sex determined by genes found on the X and Y chromosome Females: egg produced with an X chromosome Males: ½ sperm cells contain X; and the other ½ contain Y There is a 50/50 chance of child being a boy/girl Sex Determination X X X Y X X X X X Y X Y

  3. Defined: Inherited conditions found on X chromosome Usually recessive Females: XX chromosomes XH XH = healthy XH Xh = healthy carrier Xh Xh = disease Males: XY chromosomes XHY = healthy XhY = disease Rare in women (back-up X chromosome) Ex: Colorblindness, Hemophilia, Muscular dystrophy Sex-Linked Disorders

  4. Sample Colorblind Tests

  5. Hemophilia and the Royal Family

  6. What is the probability of: a. Daughter with hemophilia? 0% b. Carrier child? 25% c. Child with hemophilia? 25% d. Two healthy children? 9/16 (56%) 1 min: Discuss with your neighbor.Jen is a healthy carrier (XH Xh) of hemophilia and Adam has no history in his family (XH Y). Healthy girl Healthy boy Healthy girl (carrier) Hemophiliac boy ¾ ¾

  7. What is the probability of getting a: a. Healthy son? ½ x ½ = 25% b. Healthy daughter? ½ x ½ = 25% c. Child with hemophilia? 50% d. Carrier child? 25% Kelly does not have hemophilia even though her mother did. Jim (Kelly’s husband) is a hemophiliac. Their first child Barry is healthy but their other child Rachel is a hemophiliac. Draw a Pedigree for this family and a Punnett square for Jim and Kelly. Kelly’s mother Kelly Jim Barry Rachel Healthy girl (carrier) Healthy boy Hemophiliac girl Hemophiliac boy

  8. Sex linked recessive: Hemophilia Hint: Only 2 people are unknown.

  9. Sex linked recessive: Hemophilia

  10. Sex linked recessive: Hemophilia

  11. Review • How are sex-linked disorders different from autosome disorders? • Why are sex-linked disorders more common in males? • Write the genotype of a heterozygous dominant female. • Write the genotype of a carrier female. • Examine Kelly and Jim’s Punnett square. What are the chances they would have three children, all of whom are healthy?

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