14.0: Introduction

In which we consider how mutations can influence cellular behaviors, lead to disease, and how genes can move around within the genome, often involving the actions of transposable elements.

Up to this point, we have considered mutations that become alleles inherited from one’s parents. These parental alleles are shuffled during meiosis and upon the fusion of haploid gametes. Now we consider somatic mutations, mutations that occur during an organism's lifetime. While one's somatic cells contain the same parental alleles, the impact of these alleles will be influenced by the effects of molecular level events on their expression. A mutation that occurs within a somatic cell is passed on as part of a clone generated by asexual cell division (→). When and where a somatic mutation occurs will determine what the number and type of cells in the organism that carry the mutation. If the mutation leads to a cell lethal phenotype, cells that carry it will die, so no cells in the organism will carry the mutation. More often, somatic mutations are not lethal and can influence the rate and outcomes of cell divisions and a range of cellular behaviors.

A multicellular organism is a social system. Cells cooperate in defined ways to keep the system functioning smoothly. In particular, when and where a cell divides is under strict regulatory control, involving both internal regulatory networks, as well as signals from other cells. Some somatic mutations disrupt one or more of these regulatory networks, leading to inappropriate cell division, a behavior that underlies the appearance of tumors and metastatic cancers. Carcinogenesis itself is a complex process, involving a number of steps, a number of distinct mutations within a particular clone. While a complete study of cancer is well beyond us here, certain common features are worth considering. In particular, somatic mutations can lead to cells ignoring signals meant to control their growth and behavior. A mutant somatic cell can generate a clone that will compete with wild type clones in various ways.

---