For example, a single copy of the defective sickle-cell gene grants some protection against malaria, while a single copy of the cystic fibrosis gene offers some protection against cholera. Observe how both parents are carriers. Note that the occurrence of the disorder is not affected by the sex of the child. X-linked disorders are most common in males as there is no second X chromosome carrying the normal copy to compensate. In males therefore a recessive gene can cause a genetic disorder.
Females are less likely to be affected as they have the non-affected X chromosome as well.