Sex-Linked Punnett Squares

Sex Determination X X X Y X X X X X Y X Y 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-Linked Disorders Defined: Inherited conditions linked to the sex chromosomes Gene found on X chromosome Females: XX chromosomes XH XH = healthy XH Xh = healthy carrier Xh Xh = not healthy Males: XY chromosomes XHY = healthy XhY = not healthy Rare in women (back-up X chromosome) Ex: Colorblindness, Hemophilia, Muscular dystrophy

Sample Colorblind Tests

Hemophilia and the Royal Family

Jen is a healthy carrier (XH Xh) of hemophilia and Adam has no history in his family (XH Y). What is the probability of getting: Daughter with hemophilia? 0% Carrier child? 25% Child with hemophilia? Two healthy children? ¾ x ¾ = 9/16 (56%) Healthy girl Healthy boy Healthy girl (carrier) Unhealthy boy

Kelly is a healthy carrier of hemophilia, but Jim suffers from the disease. What is the probability of getting a: Healthy son? 25% Healthy daughter? Child with hemophilia? 50% Carrier child? Healthy girl (carrier) Healthy boy Unhealthy girl Unhealthy boy

Sex linked recessive: Hemophilia

Sex linked recessive: Hemophilia

Kobe Kuiz 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?