What are fraternal twins?

Fraternal twins are siblings conceived at the same time as two separate fertilized eggs. They are also sometimes called "biovular twins" or "non-identical twins." In fact, it is quite common for fraternal twins to define themselves in comparison to identical twins. Identical twins are two siblings born from a single fertilized egg that splits to create two fetuses. One of the key characteristics of identical twins is that they look incredibly similar or identical. Also, identical twins always share the same gender.

Unlike identical twins, fraternal twins can appear quite different from siblings at times. In fact, it's common for fraternal twins to be confused with siblings who are simply a similar age. This is especially true in late childhood, adolescence, and later in life. Also, while fraternal twins can be of the same gender, it is also possible for a pair of fraternal twins to consist of a boy and a girl. This is because, instead of sharing all of their genes like identical twins, fraternal twins share an average of 50 percent of their genes.

Another term for fraternal twins is "dizygotic twins," which is sometimes referred to in abbreviated terms as "dz twins." This simply means that the twins are the result of two zygotes instead of one, as in the case of identical twins. The zygote is the scientific term for a fertilized egg. In the case of identical twins, or "monozygotic twins," only one zygote is present at the time of conception.

Much later in life, it is possible to confuse identical twins with fraternal twins. This is because your general health, level of self-care, and lifestyle can alter the way you age. If the two members of a pair of identical twins lead very different lives, they may look more and more different as they age. Cosmetic choices like hairstyle, clothing, and makeup can also make identical twins look more like fraternal twins.

There are some groups that are more likely to produce fraternal twins than others. Dizygotic twins are more common among older mothers, especially women who conceive after the age of 35. They are also quite common in Japan and some parts of Africa. There is some evidence that dz twins are often the result of a genetic predisposition.

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