Those who inherit two copies of the mutated gene get a potentially deadly disease.

People who inherit two copies of the gene have cystic fibrosis.

We all inherit two copies (alleles) of the hemoglobin beta gene.

People who inherit two copies of the mutant gene, one from each parent, are healthy but cannot make the protein.

But when people inherit two copies of the gene, one from each parent, they often develop Tourette syndrome.

In other words, the child must inherit two copies of the defective gene (one from each parent).

The disease develops when a child inherits two copies of a defective gene, one from each parent.

A normal person will inherit two copies of such a protective gene.

Almost all cases of Down syndrome develop in children who inherit three copies of chromosome 21.

More severe cases result from inheriting two copies of the defective gene.