What is the most common genetic abnormally? Is hemochromatosis (iron overload) the most common genetic abnormally? Heterozygous (single gene) 1 in 8 Homozygous (double gene) 1 in 200 (source: http://www.emi.net/~iron_iod/io42000.html). What are the other common genetic abnormalities? E. Williams kakapo at sprynet.com