In 1909, Danish botanist Wilhelm Johanssen coined the word gene for the hereditary unit found on a chromosome. A gene is the basic physical and functional unit of heredity. Genes act as instructions to make molecules called proteins. In humans, genes vary in size from a few hundred DNA bases to more than two million bases. The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes in their body. Within cells, DNA is organized into long structures called chromosomes. These chromosomes are duplicated before cells divide in a process called DNA replication.
So when working out how many genes make up DNA the answer can be varied if a little unsure due to the huge amount of information which must be analyzed and the many variants involved. Most research and writings point to the fact that genes make up only around one to 10 per cent of DNA, though according to the well renowned Prentice Hall Biology text book 2008 edition, it claims that only two percent of DNA is made up from genes.