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| Chimpanzee |
Humans don't appear to have much in common with mice and worms. Yet within the cells of each are genes, operating instructions made of DNA. Despite the differences among organisms—wings, leaves, feet or fins—most share a surprising number of genes. Humans and one species of worm, for example, share 21% of their genes; humans and mice share 90%. Scientists compare the genes of plants, animals and humans primarily to learn more about ourselves.
| Fruit fly | 36% |
| Mouse | 90% |
| Roundworm | 21% |
| Yeast | 23% |
| Thale cress | 15% |
| Zebrafish | 85% |
| E coli | 7% |
| Chimp | 98% |
| Rat | 90% |
What We Are ComparingComparing the genetic codes of different plants and animals to the human code reveals the percentage of genes they have in common. The same genes in different organisms may not have precisely the same arrangement of A's, T's, G's and C's, but they are so similar that scientists consider them to be the same.
Our Common GenesSince genes are inherited from parents, each generation is linked to the one before. The genes we share with other living organisms were passed down from one generation to the next, starting with a universal ancestor that lived some 3.5 billion years ago. Through evolution, accidental changes in the DNA code create different species. Today, traces of ancient genes can be found within all of us, worms and humans alike.
We All Have Genes
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| DNA Helices |
Virtually every type of cell in the human body contains a complete copy of all the genes needed to "code" for a person. Genes spell out biological instructions that direct the development and maintenance of everything from eye color to the arrangement of body parts. Every living thing, from a bacterium to a whale, has genes.
Body cells contain a copy of the complete set of instructions needed for the development and maintenance of an organism. This whole set is called a genome.
Zooming in on a human cell reveals a mass of DNA contained inside the nucleus. During reproduction the DNA is organized in bundles called chromosomes.
DNA is a long string of chemical units that we abbreviate as A's, T's, C's and G's.
Segments of the DNA code form instructions that guide cell function. Each segment is called a gene.
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