Generally mono-eyed parents do not give birth to double-eyed offspring, but it is possible to have a double-eyed child if gene unexpressed or gene mutation occurs. 1. Genetic predisposition: If both parents are mono-eyed, the child will generally be mono-eyed, but some children may have double eyelids. This is because it may happen that one or both parents carry the double eyelid gene, but the double eyelid is not shown, but the double eyelid gene is passed on to the child, and it is fully shown in the child, so that the child becomes double eyelid. 2. Gene mutation: usually genes have strong stability and are not easy to produce changes, but genes can be mutated under a certain degree of internal and external environmental factors, if the parents’ germ cells or fertilized egg cells are mutated, they may give birth to a baby with double eyelids, which is relatively unlikely. 2 people with single eyelids may give birth to a child with double eyelids, but their chances are low, and you can consult your doctor for the exact genetic pattern.