Do identical twins have 100% same DNA ?

Usually we see identical twins as a complete xerox copy of each other, and often believe that they must have exactly same DNA, just because their bodies look same. But this belief is wrong. Lets look into the science of Identical twins. Identical twins come into existence from same egg cell and sperm cell. A fertilized egg cell, which is also known as zygote, splits into two separate embryos. This split takes place in first week, but in some rare cases it can also happen in 2nd week. The earlier it happens, the twins will share more similar DNA, the later it happens the similarity will be less. No matter how similar their DNA is, they won't be exactly 100% same, but almost 100% same. Why ? Betterhealthfacts.com will answer it here.

Gene Expression can make them different

It is not just our DNA or genes that decide who we are. It is the gene expression. Even twins with 100% similar DNA may have different gene expression. No matter how much their outer appearance seems similar, some of their personality traits will be different. 

All cells of our body have same DNA, even a muscle cell and a neuron cell have same DNA, but their structure and functionality are totally different. It is due to different gene expression. 

Different environmental factors and nutrition can affect gene expression. Even twins inside the same womb may get different nutrition, which can easily trigger different gene expression. To know more about Gene Expression you should read our article : Can our brain Turn ON and OFF genes as per need.

Mutation in Genes

Researches have found that identical twins may have different gene mutations. Sometimes these mutations are found responsible for genetic diseases in one of the twins. Environmental factors play an important role in gene mutation which happens at the time of DNA replication. Our whole body is a product of DNA replication, and every two individuals have different environmental factors, even if those two are residing inside the same womb.

Variation is DNA gene sequence

Dr. Dumanski, a professor of genetics at the University of Alabama at Birmingham, has recently found that sometimes there are very minor differences in DNA gene sequence of Adult twins. It is a topic of research that either those differences were present from birth or it occurred at a later stage. Such variations can sometimes save a person from some diseases and also make the person prone to some diseases.

DNA of any two human beings is 99.9% same

Yes, we are all 99.9% same. So if we say that identical twins are almost 100% same then it won't be wrong. Even some minor variations in DNA gene sequence will be so small in overall comparison that percentage wise it will be almost 100% same, because the difference can only be compared in 6 to 10 decimal places. All of us just 0.1% different from each other, but that percentage in identical twins will be a million times smaller than that.

Final Thought : It is not our DNA that makes us who we are. Apart from our DNA and genes there are a lot of other external factors which involves our nutrition, our experiences, our education, our thoughts, our interaction with others and a lot more. Even fingerprints of identical twins are never same, so how can be their personality.