14.3: Genome dynamics

Aside from the insertion of “external” DNA through horizontal gene transfer, something rare in eukaryotes or abnormal meiotic recombination events (see below), we might assume that the genome itself, is largely static. It is, however, clear that genomes are more dynamic than previously thought. In addition to the point mutations that arise from mistakes in DNA replication, different type of genomic variation were uncovered in the course of genome sequencing studies, these include the movements of transposable elements, known as “structural variants.” They include flipping of the orientation of a DNA region (an inversion) and sequence insertions or deletions, known as copy number variations.^[485] It has been estimated that each person contains about 2000 “structural variants”.^[486] Large chromosomal inversions or the movements of regions of DNA molecules between chromosomes can have effects on chromosome pairing during meiosis (described above), and can lead to hybrid sterility and inviability. The mechanisms that lead to these genomic changes are largely beyond our scope here.^[487]

As before, if new genetic variants occur in the soma, rather than the germ line, they will be lost when the host organism dies. If a mutation disrupts an essential function, the affected cell will die and likely be replaced by surrounding cells. Multicellular organisms are social systems. It is often the case that organisms have both internal (cellular) and social (organismic) systems to guard against social cheaters. Mutant, "eccentric" or "misbehaving", cells can actively kill themselves through the process of apoptosis or they can be induced to die through interactions with their normal neighbors or, in organisms with an immune system, by cells that can identify them as abnormal and induce their death.^[488]

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