Good idea, Ray!
Going back through the thread made me realize that I had been remiss in not including the Rh information in my little genetics lesson. At the time, I thought it would probably confuse matters more to include it in the same post, and stuck to the basics of ABO blood typing.
The principles for how you inherit your particular Rh factor are the same. Your Rh factor is an expression of TWO bits of genetic code, one from each of your parents.
A person with Rh negative blood has two "negative" markers. However a person with Rh positive blood can have either two "positive" markers, or one "positive" and one "negative". It's kind of like binary code where 1 = yes and 0 = no.
Two "yes's" = yes, one "yes" + one "no" = yes, two "no's" = no.
Mother | Father | Child |
Rh positive (++) | Rh positive (++) | Rh positive (++) |
Rh positive (++) | Rh positive (+-) | Rh positive (++) 75% or (+-) 25% |
Rh positive (++) | Rh negative (--) | Rh positive (+-) |
Rh positive (+-) | Rh positive (++) | Rh positive (++) 75% or (+-) 25% |
Rh positive (+-) | Rh positive (+-) | Rh positive (++) 25% or (+-) 50% OR Rh negative (--) 25% |
Rh positive (+-) | Rh negative (--) | Rh positive (+-) 25% OR Rh negative (--) 75% |
Rh negative (--) | Rh positive (++) | Rh positive (+-) |
Rh negative (--) | Rh positive (+-) | Rh positive (+-) 25% OR Rh negative (--) 75% |
Rh negative (--) | Rh negative (--) | Rh negative (--) |
The red highlighted Rh positive babies are the ones at risk for developing hemolytic disease of the newborn, and their mothers should have injections of Rhogam/Winrho during pregnancy (around 28 weeks gestation) and within 72 hours of delivery to protect against the development of antibodies in her bloodstream that would jeopardize the baby and future pregnancies.
The percentages indicate the mathematical probability of what the baby's Rh factor will be.
As a side note, many hospitals in Canada do not routinely perform blood typing on newborns, unless the mother is Rh negative and there is a possibility of Rh incompatibility or when the baby is sick and is in NICU. The rationale for so doing is that it is not felt to be the prerogative of medical profession to cast questionability on a child's paternity. I have personally seen more than one instance of a father, who was mistaken about his own blood type or did not understand the genetics of blood type inheritance, accuse the wife of cheating on him immediately after the baby was born and a blood type is performed on the baby for medical reasons, because he mistakenly believed that the baby's blood type should be the same as his own. That kind of emotional distress is completely unnecessary, particularly when it becomes established that the father was mistaken, and was in fact the baby's father, and not the product of an adulterous relationship. The father had already gone to a lawyer (within 24 hours of the birth) to initiate divorce proceedings, while the wife was still in hospital. Of course, once he realized that he had over-reacted and was wrong, the emotional damage to his wife could not be undone with a simple apology. She still had the husband move out before she went home from hospital. It was so sad and so unnecessary.
Love, Scully