In fact, single pairs are determined by parents' genes, and double eyelids are controlled by dominant genes, that is, genotype Aa or AA determines double eyelids; Single eyelid is controlled by recessive gene, that is, genotype aa determines single eyelid. The generation of single eyelid and double eyelid is related to a levator palpebrae superioris muscle of human upper eyelid. The formation of double eyelids is due to the fibers of levator palpebrae superioris muscle extending into the subcutaneous tissue, and the muscle contraction makes the skin at the attachment shrink, which constitutes skin folds, namely double eyelids, commonly known as double eyelids; The single eyelid lacks this levator muscle fiber attached to the skin, so there is no wrinkle. If a person's genotype contains the dominant gene A that controls double eyelids, then his trait should generally be double eyelids. However, in the process of individual development, due to the modification of other genes or the influence of complex factors such as internal and external environmental conditions, the development of muscle fibers of levator palpebrae superioris may be incomplete, resulting in one eye with a single eyelid and the other with a double eyelid; Others show double eyelids at a certain stage and single eyelids at a certain stage.

It can be seen that the inheritance of this trait of eyelid is influenced by complex factors such as genes and internal and external environmental conditions. In order to answer your question clearly, you can consider two situations:

1, excluding the influence of complex factors such as internal and external environmental conditions, only considering the role of genes:

1/2: Because the single eyelid is recessive, and because a child with a single eyelid is born, the couple's traits are aa and aa, so the probability of having another child with Aa is 1/2.

2. Considering the interaction of genes, internal and external environmental conditions and other complex factors, the situation is much more complicated and the probability cannot be solved. If you are a middle school student, you can know that this situation exists and you don't need to delve into it. You can master the first situation.

Double eyelid incision refers to the method of cutting the eyelid, removing muscle and fat, removing loose skin according to the situation, and connecting the dermis with levator palpebrae superioris, which supports the eyelid. Incision method is suitable for single eyelid with thick or fat, single eyelid with different sizes or ptosis. Double eyelid surgery: Also known as pc, polymer double eyelids, three-point positioning and five-point positioning, without cutting the skin, just use a suture to fix several places along the drawn double eyelid line to make double eyelids. Weifang medical college plastic surgery hospital