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Chapter 27 : Comparing Genomes
This chapter provides information about how genomes change, what kinds of questions can be addressed by comparing genomes, and general approaches to making those comparisons. The raw material for evolution, or genome change, is mutation. It is useful to think about genome changes in terms of time scales. For the genomes of two closely related individuals to be different, the changes must have occurred very fast. At this time scale, the process of recombination is extremely important. In comparisons of animal genomes, scientists have found that even between two species that are not particularly closely related, such as mice and humans, rearrangement events can be traced by identifying segments of chromosomes in which the order of genes is the same in the two organisms. To illustrate how genome comparisons can be useful, several examples from studies of dogs are rounded up. The most obvious way to compare genomes would be to sequence the genomes in question and use computers to help you understand the differences. However, sequencing the genome of an organism such as the dog is an enormous undertaking requiring years to finish. For genome comparisons, several highly variable regions are characterized, and a DNA “profile” is generated. Loci that are highly variable among different individuals are the ones that are useful for DNA typing, while those that are more constant are more useful for comparing breeds or species. A locus used for DNA comparisons is often called a DNA marker.