It is important for everyone to have unique DNA for everyperson on the planet because an important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.
Mutation is the primary cause of all genetic variation. Mutation is important as the first step in evolution, as it produces a new sequence of DNA for a particular gene, producing a new allele. Recombination, through intragenic recombination, may also generate a new DNA sequence (a new allele) for a particular gene.
What molecule??
I'm assuming the answer would be by diffusion.