Positive and Negative Blood Types

A common question about blood are the signs positive and negative beside your blood type. This actually is defined by the "RH System". The RH system is complicated because there are 30 different combinations for blood but Rh proteins are simply put in positive or negative groups. Genetic make-up determines:

plus plus: positive
plus minus: positive
minus minus: negative

Cite:

"Rh Factor - Blood Types, positive and negative, Blood Typing, Inheritance, Genetics,." Men, Pregnancy, Expectant Father, Calculator, Paternity Angel - Information Issues. Web. 08 Sept. 2009. .