I have been wondering this question for the last fourteen years and have finally decided to ask it and just live with the consequences. So here goes my question: what is the likelihood of an ab neg. Blood type male and b positive blood type female producing an ab negative male child? I am sure of paternity in my mind, but unfortunately the male party involved is not available for testing anymore, i just want to know for sure or have i been lying to myself and my son for 14 years. The gentleman i believe to be the father is a positive.? Thank you so much if you would be able to provide any information that might be useful so i can finally put this to rest. Thank you again.?
Concerned.

Dr.Sinuhe Answers:

Thank you for your question. If I understand correctly, your options for father are AB NEG and A POS? You are B POS and your son AB NEG, correct so far? To put it short, I can’t say anything certain about who the father is. The likelihood of Mr. AB NEG and Mrs. B POS to have AB NEG child is good, especially as we know that you are the mother.

Genes and blood types are somewhat complicated, but here’s how it goes. Lets start with positive/negative: you inherit one gene (NEG or POS) from your father and the other one from your mother. POS is dominant, which means that if you get a POS from another parent and NEG from the other, POS always wins. Obviously, if you get POS from both of them, your blood type is POS. In order to get blood type NEG , you need to have NEG from your father and NEG from your mother.

So, possibly your child got the other NEG from Mr. AB NEG (he is NEG/NEG) and the other from you (you are POS/NEG, we know that since your son is NEG). With Mr. AB NEG the probability of having a POS child is 50%.

Having the NEG donated by Mr A POS is also possible, if he is POS/NEG. However, we have to assume that Mr. A POS, like you, is POS/NEG, or NEG carrier, or “heterozygous”. Thus, in this respect Mr. A POS is clearly the more unlikely father (Since your son is NEG/NEG, meaning he has got NEG from his father as well as from his mother), but still possible.

A and B are both dominant, meaning that your son has got B from you and A from his father. Either of the options, Mr. A POS or Mr. AB NEG could easily have delivered this. Blood type alone is not sufficient for paternity testing, but may sometimes show prove that someone is NOT the father.

If you still can’t stop thinking about this, you need to ask yourself what might be the reason for that. Feelings of guilt, problems in marriage, believing that nature is so much more powerful than nurture, that the identity of the biological father makes a difference? Or perhaps something else. These are all very personal questions with no right or wrong answer and you are welcome to discuss the matter further in our discussion forums.