What are the chances of a child being bipolar if one parent is but not the other?

Genetic risk: Genes always come into the equation, ao there may be genetic risk without there being a specific gene that causes it. Since the brain is a biochemical "machine" it needs proper fuel so the best approach is preventive by learning the best "god made" diet for all of us.Leave out the "junk".

20%: In some families the inheritance pattern is such that a 50% chance is likely. Otherwise, the answer to your question is that each child of a father or mother who has bipolar disorder has a 20% chance of inheriting it & manifesting clinical symptoms of the disorder during childhoid, adolescence or adulthood.