What is a Genome?

A genome is all of the DNA in an organism, including its genes and a lot of DNA that does not contribute to genes. Each animal or plant has its own unique genome. Genetic DNA is the molecular code that carries information for making all the proteins required by a living organism. These proteins determine, among other things, how the organism looks, how well it adapts to its environment, and sometimes even how it behaves.

What is a Gene?

A gene is a discrete linear sequence of DNA which corresponds to a heritable trait. In more general terms, one can think of genes as the smallest unit of heredity. Analysis of the recently released Human Genome Project data indicates the human genome contains approximately 30,000 genes--only 10,000 more than a worm!

Changing the DNA sequence of a gene changes the gene's function. Such changes are the basis for a variety of heritable traits including eye color and skin color. Unfortunately, small changes in the DNA sequence of a gene such as substitution of one base for another or omission or repetition of a small segment of the sequence can change the gene's function and result in a developmental or metabolic disorder. One goal of the human genome project is to learn more about these changes in the hope that genetic disorders might be understood and treated more effectively.

What is a Chromosome?

Most of the DNA is on structures called chromosomes. With a few exceptions, each cell in the human body contains 23 pairs of chromosomes. One chromosome of every pair is inherited from each parent. An individual human chromosome is made up largely of a tightly coiled double strand of DNA, some of which constitutes genes, but most of which (~98%) does not. The function of the nongenetic DNA is not yet known.

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