Often, the remaining "normal" allele is mutated or deleted, accelerating generation of polyps.

The second "hit" results in the loss of the remaining normal allele (gene) and occurs within a particular retinal cell.

Furthermore, heterozygotes, those who have one normal allele and one coding for the disease, also show relatively shortened telomeres.

C at position 677 (leading to an alanine at amino acid 222) is the normal allele.

In the familial form, a mutated allele is inherited along with a normal allele.

So if you have a normal allele from your mom but a mutated allele from your dad, you're kind of screwed.

Individuals with one normal allele and one faulty allele are known as heterozygous.

A heterozygous individual and a person with two normal alleles (homozygous) will have a 50% chance of producing an affected child.

Transheterozygote refers to a diploid organism for which both alleles are different mutated versions of the normal (or wild type) allele.

The ideal gene therapy practice is that which replaces the defective gene with a normal allele at its natural location.