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
- both AA,
- Father is AA and mother is AO,
- Father is AO and mother is AA and;
- 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.