How is retinitis pigmentosa inherited:

"There are three ways in which RP can be inherited:
Autosomal dominant inheritance:
This is the pattern of inheritance where RP is known to exist in a family, affecting both males and females. The probability of RP being passed from an affected parent to a child is exactly 50 per cent.
Autosomal recessive inheritance:
There will usually be no known history of RP in the family but if two carriers who show no obvious symptoms have a child, there is a 25 per cent chance that he or she will have RP.
X-linked inheritance:
This is a pattern of inheritance where only males develop the disease, but female members of a family are carriers. Some carriers can develop a mild form of RP.
For example, if a man has X-linked RP, his sons will not develop RP, but all of his daughters will become carriers. These daughters will each have a 50 per cent chance of producing an affected son and a 50 per cent chance of daughters who will be carriers. This inheritance pattern is sometimes difficult to identify in a family where there have been no sons for several generations, as the faulty gene could have passed down a line of female carriers and then suddenly affect a male child."