Are there certain genes the human has that makes the person apt to being addicted to something?

I assume there are...(reason explained later)

there are two people A and B.

A is Aa(heterozygus(addicted with one dominant and one recessive allele)) and person B is aa(homozygus ressecive)


here is what the cross looks like(when they reproduce)

Code:
     _a_a_
A  |Aa_Aa|
a  |aa_aa|

that means 1:1 - 1:1 phenotype - genotype.

so, lets say my sister is heterozygus, and my brother is unknown, what is the chance that I am homozygus recessive?

is it 100%(if my brother(who is older than me) is heterozygus) or is it 50%(my brother is homozygus recessive)?

and is there anyway I can tell?

Reason:

My sister is obviously Aa(for certain reasons), and my mom is Aa(pretty sure about it, because I am aa), and my dad is aa(he has never been addicted to cigarettes or anything for that matter), and I don't know about my brother,
but me, I've never been addicted to anything in my life, which is why I assume I am aa.

if you haven't taken a biology course, this probably won't make much sense to you... but this is the easiest way I could explain it without having to type too much.


Incase you missed it, my question(s) were:

Is there a gene in the human body that controls addiction?

if so:

is there anyway you can find out which you are(heterozygus, or homozygus dominant/recessive)?


Thanks,
Dennis