If its a passive trait, then you could (in an extreme case) have all your little fry end up with this trait, and on the other side of tracks, expect that none of them end up with this trait.
Its genetics, and imo, all bets are off when you start talking about chances. There are people out there where both the parents have the same defective chromosome in their gene pool, but none of their 4 children have it. There have also been parents who had a 1 in 4 chance of having a second child with progeria, they decide to go for it, and end up with two kids who have progeria.