ABO blood group system and likely predates human migration from Africa. The O01 allele is considered to predate the O02 allele. Some evolutionary biologists theorize that there are four main lineages of the ABO gene and that mutations creating type O have occurred at least three times in humans. From oldest to youngest, these lineages comprise the following alleles: "A101/A201/O09", "B101", "O02" and "O01". The continued presence of the O alleles is hypothesized to be the result of balancing selection. Both theories contradict the previously held theory that type O blood evolved first. It is possible that food and environmental antigens (bacterial, viral, or
Cord blood bank determine Human Leukocyte Antigen type. It will also be examined for nucleated cell count, cell viability, blood group antigen ABO & Rh blood group system, molecule cluster (CD34), and bacterial and fungal growth. After the collection, the cord blood unit is shipped to the lab and processed, and then cryopreserved. There are many ways to process a cord blood unit, and there are differing opinions on what the best way is. Some processing methods separate out the red blood cells and remove them, while others keep the red blood cells. However the unit is processed, a cryopreservant is added to