The Never-Ending Story of Life by Carlos E. Semino

Author:Carlos E. Semino
Language: eng
Format: epub
ISBN: 9783030759698
Publisher: Springer International Publishing

Now, the concept of infinite lifespan of certain cell type, or what can be said “immortal” capacity, does not imply that the cell does not suffer mutations (genetic changes) over generations. In fact, as it was explained before, genetic changes are fundamental to generate diversity and therefore essential for evolution. In essence, all genetic material suffers mutations over time, different mutation rates, depending of the system, but there is not scape to that. Moreover, change itself is an important property associated with organisms’ chromosomes, regardless if they are bacteria, fungi, plants, or animals. The point is not really about the change itself but instead about the mutation rate. If the mutation rate in the genetic material is high, then the organisms might suffer big changes in their genetic material (genes), and the products of these genes, proteins, could have extensive changes that might produce massive dysfunction and eventually death. If mutation rate is very low, then the organism (and the population associated) might have low genetic variability, and their chances to survive after significant environmental chances are, eventually, low. The mutation rate is precisely adjusted in each adapted organism and depends on many factors but mainly in the capacity to found dynamic equilibrium between change and adaptation to their environment. The main cells involved in transmitting these genetic chances through generation to generation are the germline cells since somatic cells do not transmit their genetic material to the next generation. This is why germline cells are very well protected in the gonads and undergo very controlled cell division in order to generate the gametes that best adjust to the survival necessities of each species. Therefore, we can say that germline cells are the most important cells to ensure the future of the particular organism population, in terms of adaptation, survival, and evolution.

Interestingly, it has been studied—in a very precise way—the mutation rate of male and females, and it has been estimated that the mutation rate is higher in paternal DNA contributions than maternal counterparts by about 75–80%. Moreover, paternal age is an important parameter that can further increase the number of mutations that might be transmitted through the gametes to offspring [4, 5]. The reason is simple: the male germline undergoes a significantly higher number of cell divisions than the female germline, and as described above, DNA replication during cell division is one of the main sources of mutagenesis. Moreover, the majority of cell divisions in the male germline take place in the spermatogonial stem cells, which are the specific stem cells that produce sperm in the gonads during meiosis. Since men continuously produce sperm from puberty onward, this explains why the sperm quality changes over time (through the process of aging). As noted in Chap. 2, it is estimated that an average man can generate nearly 525 billion (5.25 × 1011) sperm cells during his fertile life—a number that is about 1 billion times greater than the 500 egg cells generated by the average woman.

This clearly suggests that in humans, parental age is a crucial factor in ensuring the generation of normal offspring.

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