Except for identical twins, each person’s DNA is unique. This is why people can be identified using DNA fingerprinting. DNA can be cut up and separated, forming a sort of 'bar code' that is different from one person to the next.
A gene is a section of DNA that codes for a specific protein. It is the unit of heredity, and may be copied and passed on to the next generation.
The diagram shows the relationship between the cell, its nucleus, chromosomes in the nucleus, and genes.