Genetics Northern California

Autosomal Recessive

“Autosomal” means that there are two copies of a particular gene, regardless of a person's sex.  One copy is from the egg and one copy is from the sperm. 

“Recessive” means that when BOTH copies of a gene have a harmful change (variant), it can cause a genetic condition. A person with one working copy and one non-working copy of a recessive gene usually has no medical problems. 

How is an autosomal recessive (AR) condition inherited? 

Click here for a handout on AR inheritance. 

An AR condition happens when a person inherits 2 non-working copies of an AR gene; 1 copy from the egg and 1 from the sperm. That means both parents are carriers for the same condition (same gene). When both parents are carriers, there is a 1 in 4 (25%) chance for any of their offspring to inherit two non-working copies and have the AR condition.

There are rare cases of AR conditions where only one parent is a carrier. A gene can stop working when a brand new variant happens in the egg or sperm. The other non-working copy comes from a carrier parent.  When one parent is not a carrier, future children of that couple are unlikely to have the same condition. 

Genetic terms related to AR conditions:

  • Genetic carrier: A person with one working and one non-working copy of an AR gene.
    It is normal to silently carry a few non-working AR genes. A carrier could pass on either a working copy or a non-working copy of the gene to their offspring.  This is only considered a risk when both parents carry a variant in the same AR gene. 
  • Consanguineous: This means related by blood.
    Some AR conditions are extremely rare. For these conditions, the chance of meeting a partner who carries a variant in the same gene is very low, unless the two people are blood relatives (e.g., cousins, second cousins).

Last reviewed: March 2022
Reviewed by: Kimberly Barr, MS, LCGC, Kaiser Permanent Genetics Department