It is possible for two single eyelids to produce double eyelids. The single and double eyelids of a person are inherited from the parents and are determined by genetic predisposition. It is two genes, one from the father and the other from the mother, that determine whether the eyelids are single or double. For example, A means double eyelid gene, a means single eyelid gene, two genes of double eyelid people may be pure AA, may also be heterozygous Aa, as long as the two genes have A gene, it will be double eyelid, single eyelid people have only one kind of gene, that is, aa. parents are single eyelid, theoretically two genes are aa, the child eyelid gene Theoretically, both parents are monocular and both genes are aa. In fact, it is possible that one of the parents carries the A gene for double eyelids and the double eyelids are not fully expressed and look like single eyelids. If the A gene for double eyelids happens to be passed on to the child and is fully expressed in the child, it is possible for a single-eyed parent to have a double-eyed child.