In This Chapter
Understanding what genomes do (and don't do) ^ Deciphering genomes
^ Distinguishing between coding and non-coding DNA ^ Discovering neutral mutations ^ Telling time with the molecular clock
»^volution is all about heritable changes, and DNA is the material that's »•inherited. Other chapters in this book don't go into a lot of detail about the various sorts of changes that can occur at the DNA level. Instead, they focus mostly on examples involving changes in alleles at particular loci, like changes in some bit of bacterial machinery that renders the bacteria antibiotic resistant. This simple process, whereby one of the nucleotides (A, C, T, or G) in a bacterium's genome was incorrectly copied and thus changed the bacterium's phenotype, is an example of a change at a locus from one allele to another and an example of how a new allele appears in a population.
But there are other evolutionary questions we can ask about an organism's DNA. For example, how many genes are there? It turns out organisms don't have the same number of genes. Since all organisms share a common ancestor, where did the new genes come from? What sort of evolutionary changes can result in new instructions in the organism's instruction manual? Another question is how much DNA is there, and is all of it genes? Scientists have discovered that the number varies a fair bit between organisms and not always in a way you'd expect. In some organisms, most of the DNA doesn't correspond to different genes, and in other organisms, such as ourselves, lots of the DNA doesn't seem to do very much.
The field of molecular evolution seeks to understand how these changes come about, how evolution works at the DNA level, and what understanding the details of the process can tell us about how evolution might proceed.
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