crossover, that occurs during the formation of germ cells. Genetic recombination involves exchanges of parts of homologous chromosomes (matching pairs) and results in genetic mixing between the chromosomes derived from the original parents. Together, mutation and genetic recombination provide ample opportunity for wide variance in the form and capabilities of living organisms. That said, let us first consider the concept of mutation in a bit more detail.

As we considered in the previous section, there are many physical locations within the constituent elements of cell replication of the DNA molecule in which molecular level changes can result in relatively large-scale changes in the resultant cell structure. If these changes occur within a differentiated cell, that is one of those cells that comprise the resultant organism, the changes are typically limited to that cell and its descendents. In the vast majority of cases, a change will have no effect, or it will cause the cell to die. And in most cases, the loss of a single cell will not significantly affect the full organism. However, if the change alters cell replication it can sometimes turn the cell into a virulent enemy of the full organism. Specifically, it can become a cancer. We might also consider the available mechanisms through which simple changes at a molecular level can be induced.

Probably the most prevalent form of molecular level mutations occurs spontaneously as point error in the replication process that we’ve just considered. The frequency of such mutations can be increased by exposure of the replication process to various mutagens. The most common variants of mutagens are ionizing radiation and chemicals. Thus, there is always enhanced concern with any exposure of cells during the reproductive process to sources of radioactivity or to a wide variety of mutagenic chemicals. The greatest potential for impacting succeeding generations of a species lies in modifications induced in germ cells; that is, at the very earliest stage of the construction of a new entity. If changes occur at this time, they have the potential to be conveyed into virtually every cell of the new individual. Consequently, they may, by default, be included within the germ cells for the next generation. Thus, if a change can be induced, for example in a particular base pair sequence in a germ cell DNA segment, then it will affect the resulting new organism; a mutation at the entity level rather than purely restricted to a single cell level. As we’ve noted, while certain chemicals and radiation are known to induce mutations, probably the greatest source of mutational change comes from errors in the DNA replication process itself. Although this process is moderately fault tolerant it is not guaranteed to be error free. These are concepts that we consider in relation to mechanical and cognitive processes in subsequent chapters.

However effected, the vast majority of mutations are either totally harmless or ineffective, meaning that they induce no noticeable change in the next generation, or the induced change results in catastrophic modifications of the next generation organism, rendering it unable to continue life at all. Thus, we can see that the typical evolutionary feedback to such a change is that it is bad; life in the specific form of the original generation does not continue, at least in this one offspring. If subsequent reproductive episodes of the original organism are not subject to a mutation at the germ cell level, then the succeeding generation offspring will more likely be successfully constructed. In general, it is difficult for an analysis to determine if the whole series of reproductive episodes with a specific individual have a net positive or net negative impact on continuation of the species. Rather, it is typically only by looking at the resulting population increase or decline, within a relatively stable environment over a long period of time relative to the reproductive lifetime of the species, that a determination can be made as to whether a particular mutational change is good or bad.

As was noted in the previous section’s cursory description of the DNA replication process, there are points within the replication process of somatic cells and more importantly in germ cells

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