Inheriting a specific disease, condition, or trait depends on the type of chromosome affected (autosomal or sex chromosome). It also depends on whether the trait is dominant or recessive.
A mutation in a gene on one of the first 22 nonsex chromosomes can lead to an autosomal disorder.
Genes come in pairs. Recessive inheritance means both genes in a pair must be defective to cause disease. People with only one defective gene in the pair are considered carriers. However, they can pass the abnormal gene to their children.
CHANCES OF INHERITING A TRAIT
If you are born to parents who both carry an autosomal recessive change (mutation), you have a 1 in 4 chance of getting the malfunctioning genes from both parents and developing the disease. You have a 50% (1 in 2) chance of inheriting one abnormal gene. This would make you a carrier.
In other words, if four children are born to a couple who both carry the gene (but do not have signs of disease), the statistical expectation is as follows:
One child is born with two normal genes (normal)
Two children are born with one normal and one abnormal gene (carriers, without disease)
One child is born with two abnormal genes (at risk for the disease)
Note: This does not mean that children will necessarily be a carrier or have be affected.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.