In some genetic conditions, such as fragile X syndrome, the disease-causing variant is located on the X chromosome. These are called X-linked conditions.
If a woman is a carrier of an X-linked genetic condition, she will have a normal copy of a gene on one X chromosome and a copy with a disease-causing variant on the other X chromosome. This means that her children may inherit the X chromosome with the disease-causing variant. Male children who inherit the X chromosome with the disease-causing variant are generally affected by the associated condition, whereas female children are typically unaffected carriers. In some cases, female carriers may be affected by the condition to some extent, depending on the disease or variant.