While doing a pedigree analysis of a royal family from the ancient Mayan empire, you notice that a prince with the genetic disease married a person from outside the royal family without a history of the disease in her family (i.e. she is not a carrier). Of their six children, two have the disease and four are not affected. The prince’s mother and his father also had this disease. If this disease is controlled by a single gene, then the most likely explanation for disease in the children would be: