5.3 Chromosome Mutations
o Often result from a multistep process that starts when radiation causes two double-
strand breaks in a chromosome.
After a breakage, the chromosome segment can detach, flip, and reanneal in its
original location (Fig. 5.9).
In addition to involving much larger stretches of DNA that point mutation and
gene duplications, inversions produce very different consequences
Affect a phenomenon known as genetic linkage
o Linkage is the tendency for alleles of different genes to assort
together at meiosis
o Read example of the fly on page 157
Inversions change gene order and lessen the frequency of crossing over
between homologous segments of chromosomes. As a result the alleles inside
inversions tend to be inherited.
Inversion are an important class of mutations because they affect selection on
groups of alleles
o Occurs at the largest scale possible; entire sets of chromosomes
For example: if homologous chromosomes fail to segregate during meiosis I or if
sister chormatids do not separate properly during meiosis II, the resulting cells
may have double the chromosomes of the parent cell
Mutations like these can lead to the formation of a diploid gamete in species
where gametes are normally haploid
o Organisms that have more than two chromosome sets are said to be polyploidy.
This is common in plants, but rare