|MadSci Network: Genetics|
Bridget, Identical twins do have the same blood type and you and yours sisted do. However, the Rh factor (positive or negative) may not be the same. An Identical twin is defined when a single ovum is fertilized by a single sperm followed by cell division. Therefore identical siblings are genetically identical. The Rh factor or antigen D is either absent or present in red blood cells. This is important to know because someone who is negative should never receive positive blood because they may have antibodes against the Rh antigen. So if you are positive you may not give a transfusion to your sister if she is negative. Sources "Human Physiology" by Rhoades and Pflanzer 3rd edition The Learning Channel Website Sincerely, Mike
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