text: Each person has two genes that determine their blood type. with an A+, they would have either two A+'s, or an A+ and an A-. It is the same with B+. They will have either two B+'s, or a B+ and a B-. Each parent will contribute one gene to their child. So if the parents each contribute a negative blood type (B- and A-) then the child will be AB-. Negative blood types are recessive, and need two of them to be present in order for the blood type to be the dominant one. in all other scenarios (parents both donating positive blood A+ and B+, or one parent donating positive, the other negative A+ B-, or A- B+) the child will have AB+ blood type.\n\noh, there is a possibility that each parent is carrying a recessive O gene. in the case that both parents give the child an O gene, the child will have type O blood.\n\n\ni hope this answered your question, but i am unsure what you are talking about with the 7?