Explanation:
Yes they can. An AB parent can indeed sometimes have an O child. But it is by no means common. In fact it would be fair to say that it is exceedingly rare.
The one exception is in certain Asian groups. Some of these folks have a rare version of the ABO blood type gene called cis-AB. People with this gene version have an AB blood type but can easily have an O child.
The distinction between protostomes and deuterostomes is based on differences in their embryological development. Protostomes develop their oral end from their first developmental opening, while deuterostomes have their oral end develop from the second opening on the dorsal surface.
