if you have the information about the real size of the total target population (in your case Venezuelan mestizo population .....) you can calculate the research sample size here:
http://www.surveysystem.com/sscalc.htm
But if you have don't have info about the size of this specific population than your research sample would be purposive and than the number of the respondents is not strictly defined (as much respondents as you can reach is ok)
In both the cases if the differences of the genes is important for the research than you should have (nearly) equal number of the respondents from each category (min 30 respondents from each sub-sample)