In This Chapter
^ Varying by genotype and phenotype ^ Mastering the mysteries of mutations ^ Seeing how traits are determined
£ volution can't happen without variation, but not just any type of variation will do. It must be heritable variation — that is, variation that gets passed genetically from parent to offspring. But some evolutionary forces, such as natural selection and genetic drift (covered in Chapters 5 and 6, respectively), actually cause a reduction in genetic variation over time. Fortunately, mutations — random errors in the genetic code — generate the very kind of variation that evolution needs. Despite the fact that most of the specific mutations aren't good for any organisms, mutations in general are absolutely necessary.
Variation and mutation go hand in hand, so this chapter examines both topics. And because it's always fun to see how the genes you get affect who you are, I also discuss how many of the traits you exhibit are determined by the genes you have.
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