Question

The original source of new alleles, upon which selection operates, is mutation, a random event that occurs without regard to selectional value in the organism. Although many model organisms have been used to study mutational events in populations, some investigators have developed abiotic molecular models. Soll et al. (2006. Genetics 175:267-275) examined one such model to study the relationship between both deleterious and advantageous mutations and population size in a ligase molecule composed of RNA (a ribozyme). Soll found that the smaller the population of molecules, the more likely it was that not only deleterious mutations but also advantageous mutations would disappear. Why would population size influence the survival of both types of mutations (deleterious and advantageous) in populations?

Short answer

Answer: Population size influences the survival of both deleterious and advantageous mutations in populations due to the effects of genetic drift. Genetic drift is a random change in the frequency of alleles in a population because of chance events. In smaller populations, genetic drift is more significant, which can lead to an increased prominence of deleterious mutations and the loss of advantageous mutations. This can impact the ability of the population to adapt to changing environments and evolve.

Step-by-step solution

Understanding mutations in populations

Mutations are random changes in an organism's DNA and are the original source of new alleles, which selection acts upon. They can be classified into deleterious mutations, which have negative effects on the fitness of an organism, and advantageous mutations, which have positive effects on its fitness.

Genetic drift and its effect on populations

Genetic drift is a random change in the frequency of alleles in a population due to chance events. It plays a significant role in smaller populations, as random events have a larger impact on the frequency of alleles. The effects of genetic drift in a population are the loss of genetic variability, fixation of alleles, and the potential of the population to adapt to changing environments.

Population size and the survival of deleterious mutations

In smaller populations, genetic drift has a more significant effect which can lead to a higher chance of deleterious mutations becoming fixed in the population. This can occur as a result of the random chance events outweighing the selection pressure acting against these deleterious mutations. Moreover, smaller populations have limited genetic variation, increasing the likelihood of deleterious mutations becoming prominent in successive generations.

Population size and the survival of advantageous mutations

Similarly, in smaller populations, the survival of advantageous mutations is also affected. Even if an advantageous mutation occurs, genetic drift can cause the mutation to be lost from the population due to random chance events. This prevents advantageous mutations from becoming fixed in the population, reducing the potential for adaptive evolution.

Conclusion

In conclusion, population size greatly influences the survival of both deleterious and advantageous mutations in populations. Smaller populations are more susceptible to the effects of genetic drift, which can lead to the increased prominence of deleterious mutations and the loss of advantageous mutations. This can, in turn, impact the ability of the population to adapt to changing environments and evolve.