Book Viewer

Short Contents | Full Contents | Other books @ NCBI

Modern Genetic Analysis Chapter 8. Chromosome Mutations
Introduction

Gene mutations (Chapter 7) are one source of genomic change. However, the genome can also be remodeled at a larger scale by alterations to chromosome structure or by changes in the number of copies of chromosomes in a cell. These large-scale variations are termed chromosome mutations to distinguish them from gene mutations. Chromosome mutations can be detected by microscopic examination, genetic analysis, or both. In contrast, gene mutations are never detectable microscopically; a chromosome bearing a gene mutation looks the same under the microscope as one carrying the wild-type allele. In the main, chromosome mutations have been best characterized in eukaryotes, and all the examples in this chapter are from this group.

Chromosome mutations are important from several biological perspectives. First, they can be sources of insight into gene function on a genomic scale. Second, they reveal several important features of meiosis and chromosome architecture. Third, they constitute useful tools for experimental genomic manipulation. Fourth, they are sources of insight into evolutionary processes.

Many chromosome mutations cause abnormalities in cell and organismal function. Most of these abnormalities stem from changes in gene number or gene position. In some cases, a chromosome mutation is due to chromosome breakage, and the break may occur within a gene, thereby leading to functional disruption.

For our purposes, we will divide chromosome mutations into two groups: changes in chromosome number and changes in chromosome structure. These types of changes are two fundamentally different kinds of events. Changes in chromosome number are not associated with structural alterations of any of the DNA molecules of the cell. Rather, it is the number of these DNA molecules that is changed, and this change in number is the basis of their genetic effects. On the other hand, changes in chromosome structure are novel sequence arrangements of one or more DNA double helices. We begin by exploring the nature and consequences of changes in chromosome number.

© 1999 by W. H. Freeman and Company. All rights reserved.