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Meiosis and sexual reproduction allow germ-line mutations to be passed to approximately half the members of the next generation,.

All cells carry mutation

No cells carry mutation

Meiosis and sexual reproduction allow germ-line mutations to be passed to approximately half the members of the next generation,.

All cells carry mutation

No cells carry mutation

.who will carry the mutation in all their cells.

Original DNA sequence (a) Base substitution (b) Insertion (c) Deletion

Original DNA sequence (a) Base substitution (b) Insertion (c) Deletion

17.3 Three basic types of gene mutations are base substitutions, insertions, and deletions.

Germ-line mutations arise in cells that ultimately produce gametes. These mutations can be passed to future generations, producing individual organisms that carry the mutation in all their somatic and germ-line cells (see Figure 17.2). When we speak of mutations in multicellular organisms, we're usually talking about germ-line mutations. In single-cell organisms, however, there is no distinction between germ-line and somatic mutations, because cell division results in new individuals.

Historically, mutations have been partitioned into those that affect a single gene, called gene mutations, and those that affect the number or structure of chromosomes, called chromosome mutations. This distinction arose because chromosome mutations could be observed directly, by looking at chromosomes with a microscope, whereas gene mutations could be detected only by observing their phe-notypic effects. Now, with the development of DNA sequencing, gene mutations and chromosome mutations are distinguished somewhat arbitrarily on the basis of the size of the DNA lesion. Nevertheless, it is useful to use the term chromosome mutation for a large-scale genetic alteration that affects chromosome structure or the number of chromosomes and the term gene mutation for a relatively small DNA lesion that affects a single gene. This chapter focuses on gene mutations; chromosome mutations were discussed in Chapter 9.

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