Is it possible if both parents are A positive and the baby is O positive?

3 Answers

aimeevd's profile pic

aimeevd | (Level 1) Adjunct Educator

Posted on

Absolutely.  A is dominant to type O blood.  If you are type A you can either have the genotype "AA" or "Ai", and if you are type O you will have the genotype "ii".  If both parents are heterozygous for type A blood (they both have "Ai") then one fourth of their offspring will have type O blood (genotype "ii").  (Also one half of their offsping will be "Ai" and one fourth will be "AA", 75% will have type A blood, so it is significantly more likely to be type A.)

jmaag's profile pic

jmaag | (Level 1) Adjunct Educator

Posted on

Yes, it is possible for parents to have type A blood and their child to have type O blood. The positive and negative of the blood is called the rH factor and is separate from the type of blood. There are two types of genes, dominant and recessive. Dominant genes are always expressed when they are present. Recessive genes are masked by dominant genes, but can be expressed as long as only recessive genes are present. Type A and Type B are dominant blood types. Type O is a recessive blood type. Each person has two genes for a trait, one from the mother and one from the father. 

The parents in this case have the dominant A blood type. The second gene is unknown. A punnett square can be used in this situation to determine the genotypes of the parents. Since the child has O blood, the parents must both have the recessive O trait. The child's genotype is OO and the parent's genotype is AO. This is assuming that paternity is not in question.

jerichorayel's profile pic

jerichorayel | College Teacher | (Level 2) Senior Educator

Posted on

Yes. To better explain that phenomena, we should first look at the genotypes of the blood type A. Blood type A has genotypes of AA or AO. Parents with a Blood type A+ Can either have

  1. both AA,
  2. Father is AA and mother is AO,
  3. Father is AO and mother is AA and;
  4. Both AO.

Case 1: If both of them have the genotype of AA, there is a zero possibility that their children would have a blood type of O since there is a 100% AA genotype for their children.

Cases 2 and 3: If one of them is AO and the other is AA, their children would bear genotype possibilities of 50%AA and 50%AO

Case 4: If both of the parents have a genotype of AO then there is a chance that their children would have a blood type of OO since the resulting genotype would be 25%AA, 50%AO and 25%OO.

But since we do not know if the parents have homozygous (AA) or heterozygous (AO), we can add all the possibilities (the four cases). By doing that, we can have a total of:

AA = 56.25%

AO = 37.50 %

OO = 6.25 %

Since AO and AA is Blood type A, then we have a total of 93.75%A and 6.25%O which means that there are small but POSSIBLE chances that their children would bear a blood type O.