Right at the start of development, a single egg gets fertilized by one sperm, giving rise to identical twins. Then, when the zygote is just a tiny cluster of cells, it splits into two. At this early stage, both babies have exactly the same genetic material.
In cases where a mother receives fertility assistance, identical twins can still happen. If one of the fertilized eggs is put back into her uterus and it divides, identical twins are formed.
It's important to note that a couple's country, ethnicity, or race doesn't influence the likelihood of having identical twins. Every couple has an equal chance of having identical twins; it's not tied to any specific factors. In fact, the odds of having identical twins are about one in every three sets of twins. The remaining two-thirds of twins are non-identical.