 [ Symptoms ] 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 [ Disease ] 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 do not 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 is not possible