Putting DNA to Work
  INTRODUCTION

Tracing Similarities And Differences In Our DNA

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What percent of their genes match yours?

Another human? 100% - All humans have the same genes, but some of these genes contain sequence differences that make each person unique.
A chimpanzee? 98% - Chimpanzees are the closest living species to humans.
A mouse? 92% - All mammals are quite similar genetically.
A fruit fly? 44% - Studies of fruit flies have shown how shared genes govern the growth and structure of both insects and mammals.
Yeast? 26% - Yeasts are single-celled organisms, but they have many housekeeping genes that are the same as the genes in humans, such as those that enable energy to be derived from the breakdown of sugars.
A weed (thale cress)? 18% - Plants have many metabolic differences from humans. For example, they use sunlight to convert carbon dioxide gas to sugars. But they also have similarities in their housekeeping genes.

Why Were Genes Used In This Comparison, and How Do They Relate To DNA?

Genes are the fundamental units of DNA function. In DNA terms, genes are discrete sections of the DNA sequence that are part of much longer DNA molecules. They provide the biochemical instructions for producing all of the components of biological organisms. Some genes specify visible physical traits, while others govern metabolic processes. Most traits, such as the shape of your face, require the actions of many genes.

Why Are We So Similar?

The DNA of these species is so similar because the basic organization of life is widely shared, with the largest differences found between plants and animals, or between tiny single-celled organisms like yeast and large multicellular organisms like ourselves. The similarities reflect a common ancestry that appears to be shared by all life on Earth.

Are People Really Identical?

Even though humans share 100% of the same genes, the instructions contained within the genes are not entirely identical. Each person is unique. People have different hair colors, facial structures, and other traits. These differences between individuals result from very small differences in their DNA sequences. DNA also contains many so-called "housekeeping genes" that control important metabolic processes. As you will see, some of the differences in these genes can cause illness.

Although the DNA of any two people on Earth is, in fact, 99.9% identical, even a tiny difference can have a big effect if this difference is located in a critical gene.


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