All living organisms store genetic information using the same molecules — DNA and RNA. Written in the genetic code of these molecules is compelling evidence of the shared ancestry of all living things. Evolution of higher life forms requires the development of new genes to support different body plans and types of nutrition. Even so, complex organisms retain many genes that govern core metabolic functions carried over from their primitive past

Hello Zara,

I don't know how to answer your question because organisms having identical DNA are rare. But recently I read an article which can be relevant to your question. https://www.sciencedaily.com/releases/2012/04/120409164426.htm

I also read an article from the year 2008 where they have claimed that identical twins have identical DNA

https://www.nytimes.com/2008/03/11/health/11real.html Hope you get an idea from what I shared :)