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 X H X H = healthy X H X h = healthy carrier X h X h = not healthy Males: XY chromosomes X H Y = healthy X h Y = not healthy Ex: Colorblindness, Hemophilia, Muscular dystrophy

Sample Colorblind Tests

Hemophilia and the Royal Family

Jen is a healthy carrier (X H X h ) of hemophilia and Adam has no history in his family (X H Y). What is the probability of getting: Daughter with hemophilia? 0% Carrier child? 25% Child with hemophilia? 25% Two healthy children? ¾ x ¾ = 9/16 (56%) Healthy girlHealthy 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? 25% Child with hemophilia? 50% Carrier child? 25% Healthy girl (carrier) Healthy boy Unhealthy girl Unhealthy boy

Sex linked recessive: Hemophilia

Quick Review Sex linked disorders are found on the sex chromosomes Males more at risk due to have only one X chromosome Females carriers are normal, but can pass trait to future generations