Answer is 'b' i.e. 16 and 4 Three forms of ADPKD have been identified. ADPKD-1 - accounts for 85% of cases - its gene is found on chromosome 16p ADPKD-2 - its gene has been mapped to chromosome 4q - it appears to have a later age of onset of symptoms and renal failure than ADPKD-1 ADPKD-3 - it has not been mapped to a gene uptill now.