Chapter 4: Mutation and Genetic VariationOverview |
Mutation is the ultimate source of the heritable variation that must be present for natural selection and the other evolutionary processes to act. Chapter 4 of your textbook has two goals: to investigate the mechanisms responsible for generating new alleles and new genes, and to explore how biologists quantify the amount of genetic variation that exists in natural populations.
4.1 Where New Alleles Come From The instructions for making and maintaining an organism are encoded in its hereditary material—the molecule called deoxyribonucleic acid, or DNA. DNA is made up of smaller molecules called deoxyribonucleotides. The four deoxyribonucleic acid ribonucleotides found in DNA are similar in structure: Each contains the 5-carbon sugar called deoxyribose, a phosphate group, and a distinctive nitrogen-containing base.
Turn to section 4.1 to learn about the structure of our ultimate hereditary molecule.
4.2 Where New Genes Come From Several kinds of mutations can create new genes, just as several types of mutations can create new alleles. Gene duplications are probably the most important source of new genes, however.
Turn to section 4.2 to learn about the variety of mechanism that give rise to new genes.
4.3 Chromosome Alterations A wide variety of changes can occur in the gross morphology of chromosomes. Some of these mutations affect only gene order and organization; others produce duplications or deletions that affect the total amount of genetic material. They can also involve the entire DNA molecule or just segments.
In section 4.3 of your textbook you can learn about two types of chromosome alterations that are particularly important in evolution.
4.4 Measuring Genetic Variation in Natural Populations In the previous three sections of this chapter, we discussed the processes that generate new alleles, genes, and chromosomes. These processes create the genetic variation that is the raw material for evolution.
Turn to section 4.4 of your textbook to explore the methods that biologists use to measure the amount of genetic variation present in natural populations.