The double helix (on the left) is an illustration of one DNA. Examining further (on the right), the back bone of each of the helices is a sugar-phosphate moluecule.
… sugar-phosphate-sugar-phosphate-sugar-phosphate …
Each sugar on one helix bonds with one sugar on the other helix through its nucleotide.
DNA in humans is very long, 3 Billion nucleotides long. We’ve all heard DNA is the element that makes us who we are, it is our genetic code. Imagine the variations of human beings that can be. With 4 different nucleotides, an animal whose DNA is 3 nucleotides long can have 4x4x4x4 i.e., 256 possible individuals. In humans, that variance is unimaginably enormous, 43000000000
If there are so many possible different DNAs, why do we all have so many similarities? Human beings are so similar to each other that it’s quite easy to identify someone as a human being even if we never saw that person before. Turns out, 99.9% of the human DNA is identical. Yes, it’s just the 0.1% of our DNA that makes us unique.