Genes are the basic unit of heredity. A gene is a sequence of nucleotides containing information on specific traits that shape the characteristics of an organism. Each person actually has two copies of each gene; one comes from each parent. There’s not really a “typical size” for a gene, since the number of base pairs in a gene can range from just a couple hundred base pairs to millions of base pairs. Most of the genetic information in each of our genes is actually the same from person to person. In fact, differences in less than 1% of the DNA in our genes accounts for all of the physical differences between people.