Most of us are aware of what twins are: two persons born of the same pregnancy who share genetic similarities. Twins are generally categorized as being either identical or fraternal. Identical twins are characterized as having genetic blueprints which are carbon copies of each other.
Identical vs. fraternal twins
In cases of identical twins, or monozygotic offspring, the twins are a result of the same fertilized egg separating into two exact copies of itself. When this happens, both of the twins will share the exact same genetic makeup meaning they have identical copies of one another’s DNA. This results in two children who will appear as mirror images of each other. Identical twins will always be of the same sex, for example two male children or two female children. It has been theorized that identical twins are the result of the formation of a blastocyst which subsequently collapses causing the fertilized egg to split into two copies, each forming an egg mass which will develop into a fetus in a shared placenta. Identical twins can also now with today’s technology be formed artificially by manually splitting the egg in a laboratory prior to embryonic implantation. Identical twins are estimated to occur in just three out of every one thousand births.
We are also aware of cases where twins born are not identical, but rather fraternal twins. These are referred to as dizygotic twins in the scientific community. Fraternal twins are not identical biologically, even though it’s possible that they may appear very similar in appearance just as siblings of the same parents oftentimes do. Fraternal twins are unique in that they do not originate with the same fertilized egg, nor share the same placenta. Fraternal twins are essentially two siblings whose conception occurs simultaneously in the womb of the mother, each sharing biological traits but not exact copies of genetic material. Finally, fraternal twins can be of the same sex, or in other cases one female and the other male.