At least 500 human traits are definitely known to show an autosomal recessive inheritance pattern (as opposed to dominant inheritance); men and women are equally affected, though some conditions are more common for people from specific ethnic backgrounds.
An autosome is a non-sex chromosome, of which there are 44 in each human cell. Now we get two copies of every gene from our parents; one from our father and one from our mother. If there is a mutation on one gene and it doesn’t cause a disease it is said to be recessive. And a recessive pattern of inheritance means it becomes a problem only if both copies of the gene for a particular trait has a mutation. Someone who has just one mutated gene for this trait is said to be a carrier, and they show no signs of having the disease. There are millions of people around the world who are carriers for genetic diseases and they know nothing about it. They usually find out if they have a child that is born with a condition; and that’s because their partner also has the same recessive mutation.
If both parents are unaffected carriers for a condition, there is a 25% chance that a child will inherit the mutated gene and be born with the condition or have a genetic predisposition to it. If only one parent is a carrier, there is no chance that a child will inherit the condition or be predisposed to it.
Autosomal recessive traits are of particular interest in genetic counseling. Examples of autosomal recessive conditions are cystic fibrosis, Tay Sachs disease and sickle cell anemia. Most often the relatives of an affected person seek advice about whether they are carriers or about the chances of them having an affected child. It is sometimes possible to infer a person’s genotype directly from pedigree studies, and the person can thereby be told his or her status as a carrier. But even when a person’s genotype cannot be deduced by pedigree analysis, it is often possible to determine it by performing various physiological and biochemical tests.
This post is part of the series: Mendelian Inheritance in Classical Genetics
Learn about Gregor Mendel’s Laws of Inheritance, and about autosomal dominant and recessive genes.