this is an interesting question. blood type is inherited from genes contributed by each parent. in order to produce offspring with type a blood at least one parent must also have type a blood. two parents with type o blood can only produce offspring with type o blood. it gets a little complicated because for example genetically speaking two ab type parents can produce offspring with type o blood. it may also be possible for an ab type parent to contribute the a type to offspring when the other parent contributes the o gene. if either the mother or the father has type o blood the other parent must have type a blood (or possibly type ab) to produce offspring with type a blood. the positive (+) and negative (-) signs related to blood type refer to the presence or absence of rh antibodies in the blood and don't affect "blood type " per se. so when considering genetic inheritance you can set aside the rh positive or negative aspect and simply look at the a-b-o system. in the end the only way to determine parentage is by genetic testing. hope you find this information useful! my mother is ab- blood my father is o- blood. i have o+ blood. does this mean my biological father is o+ blood? can 2 negatives make a positive? i had read somewhere on line that it isn't possible.
im a blood type my mother is o- and my sister is o- and the guy i was told that was my father is o- is it possible