Chemical make up of DNA
There are chemical units
in DNA called nucleotides. When these nucleotides are chemically bonded
they form chain like molecules called poly nucleotides. Each single nucleotide
has a compound called phosphate, (a compound is a combination of two or
more elements) a sugar called deoxyribose and a compound called a base.
The phosphate and sugars are the same in all DNA nucleotides, but the bases
aren't. Thymine, adenine, guanine, and cytosine are the four DNA bases.
These combine to encode a large number of different genes. The human genome
(all the human genes) has about 3 billion genetic letters (A T C and G).
The way they are arranged determines a person's genetic code. Without this
diversity we'd all look the same.