DNA is the genetic material in most organisms except in retrovirus or RNA virus.
The DNA has the coded information for the phenotypic expressions and this coded information is heritable that can be passed on from one generation to the next.
99% of the DNA is similar in humans and the 1% variation is observed in the chromatin fibers present in the telomeric regions of the chromosome.
Therefore, two people even if they are twins cannot have an identical set of DNA.