Question

What is the difference beween identical twins and fraternal twins? How do they form their genetic makeup?

Answer 1

Identical twins are natural genetic clones born together, i.e. they share same origin, same placenta and same womb at same time.
Fraternal twins are siblings who just share the womb, not the genotype.

Explanation:

Sometimes an early embryo (formed after an egg is fertilized by a sperm), splits into two separate embryos which then develop as separate foetuses. In such case as the genetic format of the two is same, they develop as two identical twins.

However, sometimes ovary releases two eggs, which get fertilized by two different sperms and two separate embryoes are formed. As they develop from different egg-sperm combinations, they are not identical and are called fraternal twins. They can have different sex too.