Chances of a child being ADHD if one parent is

I have read that ADHD is genetic and often runs in families. Even though my mother has passed on I am convinced that she had ADHD and that at least 1 of my sisters also is ADHD. (My mom was never diagnosed and my sister can't afford to be diagnosed.) Anyway, I wasn't diagnosed until 30 years old because I really never knew anything about ADHD. I could never explain my problems until I read an article in a magazine and it all clicked.

Anyway, I'm wondering if anyone knows the chances of a child being ADHD if one parent is. I do have a 3 year old and wiil have another in a couple years. As a child I was more the unfocused dreamer type, not hyperactive. I did manage to cope all right throughout my life. The last 5 years had been a battle and my symptoms got worse as I added more stress to my life (graduating college, starting a new career, getting married, buying a new home, starting a family...) I am on medication now and my husband says he has noticed a big difference and can tell when I've forgotten to take my meds.

But, I worry about my son. Are there signs I should watch out for? Is there an age when the symptoms generally begin to emerge? Knowing what I have had to go through in my life I would like to catch this early to make his life easier. Although I really do hope it's not an issue for him.