Genetic Structure - Page 2

Genes

A gene is the basic physical and functional unit of heredity. Genes, which are made up of sequences of DNA, act as instructions to make molecules called proteins.

In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes.

		Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people.
Image from The Genetics Home Reference, NIM, NIH http://ghr.nlm.nih.gov/handbook/basics/gene

The messages hidden in your genes constitute the building instructions for your appearance and everything else about you - from how your muscles function and how your eyes blink to your blood type and hair color.

Your genes are expressed through a complex system of interactions that begin with copying DNA messages into a somewhat temporary form called RNA (see RNA explanation later in this section).

RNA carries the DNA message through the process of translation, which in essence is like taking a blueprint to a factory to guide the manufacturing process. Where your genes are concerned, the factory makes proteins (from the blueprint) that get folded in very complex ways - to make "you".