With a single-celled organism such as a bacterium or yeast, all genome alterations that are not lethal or reversible are inherited by daughter cells and become permanent features of the lineage that descends from the original cell in which the alteration occurred. As we will see in Chapter 15, all events that are not lethal have the potential to contribute to the evolution of the genome but for this to happen they must be inherited when the organism reproduces.

Other mutation and recombination events have a less significant impact on the phenotype of the cell and many have none at all. A mutation in a key gene may cause the cell to die if the protein coded by the mutant gene is defective ( Section 14.1.2), and some recombination events lead to defining changes in the biochemical capabilities of the cell, for example by determining the mating type of a yeast cell or the immunological properties of a mammalian B or T lymphocyte. (B) DNA repair corrects mutations (more.)īoth mutation and recombination can have dramatic effects on the cell in which they occur. A point mutation is shown but there are several other types of mutation, as described in the text. (A) A mutation is a small-scale change in the nucleotide sequence of a DNA molecule.