A child born to a mono-eyed father and a double-eyed mother may be either mono-eyed or double-eyed. The gene for double eyelids is genetically dominant. If A and a are used to represent the dominant and recessive genes for double eyelids, the father’s gene is aa and the mother’s genes can be AA and Aa. 1. The mother’s gene is AA: in this case, all children have double eyelids and the gene is Aa. 2. The mother’s gene is Aa: in this case, the child may have single eyelids and the gene is aa, or double eyelids and the gene is Aa. Double or single eyelids are genetically determined and can occur in children. Parents should not be too concerned about whether their children have double eyelids or not, but should ensure that their children are healthy and free from abnormalities.