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Setting the scene
Published in Jessica Mozersky, Risky Genes, 2012
The founder effect is a process of genetic drift that results from a founder event. A founder event occurs when a population has a small number of founding ancestors who are separated from the larger parent population and go on to found a new population (Stone et al. 2007). Alternatively, a founder event can be the result of an extreme reduction of a population, by over 50 per cent, due to famine, war, epidemic or some other event that causes a significant number of a population's members to die. This is known as population bottleneck because the population suddenly contracts. In both of these situations, the new founding population carries only a fraction of the original population's genetic variation and is not representative of the entire diverse population from which it was derived but only a small portion of it (Goldstein 2008, Stone et al. 2007). As a result this new population can be quite distinct from the original population. The founder effect occurs when at least one of the members of the new founding population carries a genetic mutation which is then passed on to future generations. The mutation may substantially increase in frequency if the population remains reproductively closed, for example due to cultural practices such as endogamy. Members of founding populations tend to live in close geographic proximity and so are more likely to mate with one another, which will increase the frequency of the mutation as the population increases in size (Bamshad et al. 2004).
Biology of microbes
Published in Philip A. Geis, Cosmetic Microbiology, 2006
The development of tolerance for many biocides is more likely a result of phenotypic changes by which the population shifts to higher capsule production. This approach is a directional selection mechanism: the biocide forces a population bottleneck that allows survival of only a few hardy cells that pass on the genes for survival to their offspring (e.g., genes that express more frequently for capsule production). This is analogous to the proposal that the hairy elephant population gets hairier during an advancing ice age. Another mechanism allows cells to begin a primitive form of communication as in quorum sensing to stimulate physical community developments within biofilms in which a form of “cooperation” that can provide protection for the populations within the biofilm exists.6
Malaria transmission blocking compounds: a patent review
Published in Expert Opinion on Therapeutic Patents, 2022
Sara Consalvi, Chiara Tammaro, Federico Appetecchia, Mariangela Biava, Giovanna Poce
Transmission-blocking compounds are able to prevent a mosquito from infecting a human. The transition from host to vector, and vice versa, is a population bottleneck in the Plasmodium life cycle. Compared to asexual stages, the number of circulating parasites undergoing sexual development can be 7 orders of magnitude lower [19–21], and it has been estimated that only 50–100 gametocytes out of the thousands ingested by a mosquito during a blood-meal develop into ookinetes, which ultimately result in less than five parasites per mosquito at the oocyst stage. This reduction in numbers is due to several factors, including the fact that the parasite transition from intracellular to extracellular forms makes it more vulnerable to the attack of host immune factors. Indeed, the latter can mediate their killing not only in human host circulation, but also in the vector midgut, where they retain their activities for hours after the ingestion [22].