Around 9 million twins are known worldwide out of the total world population of 6,706,993,152. This clearly shows that twins are a rare occurrence. There are two types of twins- fraternal twins or identical twins. Fraternal twins are formed when two ova, or female eggs, are fertilised by two sperm cells from the male. The sperm cells can even come from different individuals. Fraternal twins are sometimes referred to as false twins since they are more similar to siblings or half siblings in their DNA profiles. Identical twins, the product of a single fertilisation between one sperm and one ovum with a split of the egg formed at a later stage, have identical genetic profiles. Identical twins are referred to as monozygotic twins and fraternal twins are referred to as dizygotic twins. Twins that appear to be identical in their facial features are not necessarily identical twins. Should one wish to find out whether twins are identical or fraternal, they can do so by doing a Twin Zygosity Test. This type of test is far more than simply informative.