Peter and Victoria are both carriers of a serious autosomal recessive disorder that is lethal in early childhood. They want to have a child who is healthy so they have a preimplantation genetic diagnosis. The test shows that their child will not have the disease, but when she is born it turns out she does have the disease. What could have happened in this situation?

a. The cell that was tested in the preimplantation genetic diagnosis had a mutation causing it to be different from the rest of the cells in the embryo.
b. The embryo mutated during development from the initial time of the testing to develop the disease.
c. The preimplantation genetic diagnosis is only accurate for non-lethal diseases.
d. Either Peter or Victoria is actually homozygous recessive.