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?

Verified step by step guidance

1. Understand that population size affects genetic drift, which is the random fluctuation of allele frequencies in a population independent of natural selection.
2. Recognize that in small populations, genetic drift has a stronger effect, causing alleles (both deleterious and advantageous) to be lost or fixed by chance more rapidly than in large populations.
3. Consider that advantageous mutations, although beneficial, can be lost in small populations because the random sampling effect can override the selective advantage.
4. Similarly, deleterious mutations might also be lost quickly in small populations due to drift, but sometimes they can become fixed if selection is weak and drift is strong.
5. Conclude that population size influences the survival of mutations because in small populations, random chance (genetic drift) plays a larger role than selection, affecting the fate of both deleterious and advantageous mutations.

Key Concepts

Mutation as a Source of Genetic Variation

Mutations are random changes in the genetic material that create new alleles, providing the raw material for evolution. They can be neutral, deleterious, or advantageous, and occur independently of an organism’s fitness. Understanding mutation is essential because it introduces genetic diversity upon which natural selection and genetic drift act.

Genetic Drift and Population Size

Genetic drift is the random fluctuation of allele frequencies in a population, which has a stronger effect in small populations. In small populations, chance events can lead to the loss or fixation of alleles regardless of their selective advantage or disadvantage, causing both beneficial and harmful mutations to disappear more easily.

Natural Selection vs. Random Effects in Evolution

Natural selection favors advantageous mutations and removes deleterious ones based on their impact on fitness. However, in small populations, random effects like genetic drift can overpower selection, making survival of mutations less dependent on their selective value and more on chance, explaining why both types of mutations may be lost.