X linked conditions are passed down on the X chromosome, therefore affecting males and females differently. Males have one X and one Y chromosome, while females have two X chromosomes.

Female carriers have a 50% chance of passing down the X chromosome with the genetic mutation to their children, and a 50% chance they will pass down the healthy X. If they pass the mutation to their sons, these boys will be affected with the condition, but if they pass the mutation to their daughters, they will usually just be a carrier of the condition. Female carriers of X linked conditions can sometimes show some signs of the condition.

Males can’t be carriers of X linked conditions. If males are affected with the condition, they will always pass the faulty gene to their daughters on their X chromosome, making them carriers of the condition. They will always pass their healthy Y chromosome to their sons, therefore male to male transmission is not possible with X linked conditions.

Fragile X syndrome and Haemophilia are examples of X linked conditions.