Chromosome Mutations

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Biological Sciences
Malcolm Mac Kinnon

5.3 Chromosome Mutations  Inversions 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  Genome Duplication 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
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