Estimating dizygotic/monozygotic ratio of twins by general formula

Eight general formulas are presented for estimation of the dizygotic/monozygotic ratio (DMR) for twins of the same sex and blood groups. The derivation of these formulas and example applications for each are given in plain English without complex statistical symbols. The formulas cover all blood group systems including multiallele systems with silent gene(s) as well as the HLA system. Predetermined DMR values for commonly used genetic markers (except HLA) are provided for U.S. white and black persons.