Clarifying Q & A
In the general population, the incidence of a brca1 mutation is between 1:500 to 1:800.
It is much lower for brca2. For a woman or offspring to inherit the gene from a parent who has one copy of the mutated gene, there is a 50% chance of acquiring the gene in question. It is autosomal dominant and therefore can manifest its deleterious consequences by itself without need of a second copy.