There are a total of 46 chromosomes or we can say 23 pairs of chromosomes. Here, the 23rd pair of chromosome decide the sex of a child and the 22 pairs are called as autosomes which are same in both men and women.
Girls have XX chromosomes, while boys have XY chromosomes. When one X egg is fertilised by an X sperm and the other by a Y sperm, girl-boy twins are produced.
Identical Twins
Monozygotic twins are identical twins. They develop from a single fertilised egg or zygote. The zygote divides into two pieces, and each piece grows into a separate embryo. They share the same DNA because of their same genetic background.
Fraternal twins
Dizygotic twins are fraternal twins. They are created when two separate sperms fertilise two eggs. Just like any other sibling born at a separate period, they share 50% of their genetic features.
Difference between Identical and Fraternal Twins :
1. Identical twins have the same sex while the fraternal twins have the same or different sex.
2. Identical twins have the same characteristics whereas fraternal twins may or may not have the same characteristics.
3. We cannot distinguish between the identical twins but fraternal twins can be distinguished.
4. Same blood type is shared by identical twins however, fraternal twins may or may not share same blood type.
5. Identical twins could be dichorionic and diamniotic or not and fraternal twins are both diamniotic and dichorionic.