Autosomal recessive inheritance

Recessive inheritance. Photo: US Nat. Library of Medicine

With a few exceptions, we all inherit two versions of each of our genes (known as ‘alleles’), one from each parent.

The role that each gene pair plays in our bodies is the same, but tiny differences in the code of their DNA result in subtle differences.

For example, we inherit a gene for eye colour from both our parents. But we might inherit the version for blue eyes from our mother and the version for brown eyes from our father.

So why doesn't this make our eyes browny-blue? It's because the allele for blue eyes is ‘recessive’ to the gene for brown eyes.

If you receive one gene for each colour you'll have brown eyes because the effects of the blue-eyed gene are masked by that of the brown-eyed one.

In autosomal recessive inheritance a genetic condition develops when you inherit a copy of a faulty gene on a non-sex chromosome from both your mother and father.

Carriers, who only inherit one of the faulty genes, don't have any symptoms because they received one of these altered genes from one parent and a healthy copy of the same gene from the other parent.

Primary immunodeficiencies, such as many types of complement deficiency and ataxia telangiectasia, are inherited in an autosomal recessive pattern.