Genetics Northern California

X-linked Recessive

X-linked recessive conditions are caused by changes in genes located on the X chromosome.  These conditions most often affect XY males.   

Click here for a handout on X-linked inheritance

Humans have two sex chromosomes, the X and the Y. Females usually have two X chromosomes. Males usually have one X chromosome and a Y chromosome. Most genes on the X chromosome are not found on the Y chromosome. When a gene on the X chromosome is not working right, it often affects males and females differently.  

  • A person with two X chromosomes usually has a second copy of the same gene that works. This protects against symptoms of the condition. These people are called carriers because they carry a non-working gene but do not have symptoms.  
  • A person with only one X chromosome only has one copy of the gene. If the gene is not working right, it can cause a genetic condition.  

When a carrier has children, there is a 50% chance to pass on the non-working gene.  Any XY male who inherits the gene will be affected. Any XX female who inherits the gene will be a carrier (usually unaffected). There is also a 50% chance to pass on the working gene. Any child who inherits the working gene will not have the condition and cannot pass it on. 

An XY male who has an X-linked recessive condition passes the X chromosome to all his female (XX) children. His male (XY) children inherit the Y chromosome instead of the X chromosome.  None of his male children will inherit the condition from him.

Last reviewed: March 2022
Reviewed by: Kimberly Barr, MS, LCGC