Can two O-positive parents have an O-negative baby?
(O-negative is the universal doner, right?)
yes, if the parents are both hetero for the Rh markers (each having one postive and one negative). heteros will still show up as Rh+
http://www.biology.arizona.edu/human_bio/problem_sets/blood_types/rh_factor.html
you can use the blood type caluclator on that page to find out blood type possibilities for your kids.
Okay. So as a crude example, it might be like blue eyes where if the mother and father both have one brown and one blue thingamajig, they’ll both be brown eyed but the child can be blue eyed. Thanks!
In general, it’s possible for two parents with a dominant trait to have a child with the recessive trait. Rh positive is a dominant trait, as are dark eyes and dark hair.