SexLinked Punnett Squares Sex Determination Sex determined by

Sex-Linked Punnett Squares

Sex Determination • 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: Recessive inherited conditions linked to the sex chromosomes • More common in males; very rare in females • Usually passed from mother to son • Females: XX chromosomes XH XH = healthy XH Xh = healthy carrier Xh Xh = not healthy • Males: XY chromosomes XHY = healthy Xh. Y = not healthy • 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: Healthy girl (carrier) Healthy boy Unhealthy boy Daughter with hemophilia? 0% Carrier child? 25% Child with hemophilia? 25% Two healthy children? ¾ x ¾ = 9/16 (56%)

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

Sex linked recessive: Hemophilia

Kobe Kuiz 1) How are sex-linked disorders different from autosome disorders? 2) Why are sex-linked disorders more common in males? 3) Write the genotype of a heterozygous dominant female. 4) Write the genotype of a carrier female. 5) Examine Kelly and Jim’s Punnett square. What are the chances they would have three children, all of whom are healthy?