Question

The microevolutionary factor most sensitive to population size is a. mutation. b. migration. c. selection. d genetic drift. e. all of the above.

Short answer

The microevolutionary factor most sensitive to population size is genetic drift.

Step-by-step solution

Understanding each factor

Mutation refers to a change in the DNA sequence within a gene or a chromosome of an organism resulting in the creation of a new character or trait not found in the parental type. Migration refers to the movement of genes from one population to another. Selection is the favoring of certain pheno/genotypes because of their effect on survival and reproduction. Genetic drift is the random variation in allele frequencies due to statistical chance.

Analyzing each factor's sensitivity to population size

Mutation rate is generally accepted as being independent from population size. Migration would rely on population size, but it is also heavily influenced by geographical factors. Natural selection would not directly depend on the size of population, it is more about the reproductive success of individuals rather than the overall number. Genetic drift, however, is highly sensitive to population size. In smaller populations, random variations can have a big impact. The larger the population, the less impact random variations will have, thus demonstrating a sensitivity to population size.

Deciding on the answer

From the analysis above, genetic drift is found to be the most sensitive to population size.

Key concepts

Genetic Drift

Genetic drift is a microevolutionary process that plays a pivotal role in shaping the genetic makeup of populations, particularly smaller ones. Unlike the other factors such as mutation, natural selection, or migration, genetic drift operates randomly, affecting how alleles (variant forms of a gene) are passed on to the next generation.

It is akin to flipping a coin – the outcome is chance-based. In small populations, such a coin flip can result in significant changes in allele frequencies from one generation to the next. This is because there are fewer individuals to contribute to the gene pool, making it more susceptible to fluctuations that can lead to an allele becoming more common or disappearing entirely. Over time, genetic drift can cause isolated populations to diverge genetically, leading to speciation.

Impact on Small Populations

For small populations, genetic drift can be a powerful force. For instance, if a certain allele in a small population happens to increase purely by chance, its prevalence can significantly alter the population's genetic composition. This phenomenon is most noticeable in isolated environments where the gene pool isn't refreshed regularly through migration.

Mutation

Mutation refers to any change in the DNA sequence of an organism. It can occur due to errors in DNA replication, the influence of external factors like radiation, or the impact of certain chemicals. Mutations can result in new traits that either offer an advantage, disadvantage, or have no noticeable effect on the organism’s survival or reproduction.

While mutations are random events, they are crucial for introducing genetic variation into a population. Without this variability, populations would lack the raw material for evolution to act upon. Mutation rates are generally constant and do not rely on population size, making mutations a less direct factor in altering allele frequencies compared to genetic drift. However, the accumulation of mutations over generations can significantly influence the genetic diversity and adaptability of species.

Source of Genetic Variation

Mutations are the original source of genetic variation that provides the diversity upon which natural selection can act. They can lead to new adaptations to changing environments, ultimately affecting the evolutionary trajectory of species.

Natural Selection

Natural selection is often described as 'survival of the fittest', but it is better understood as the differential survival and reproduction of individuals due to differences in phenotype. It is a non-random process by which favorable traits, which increase the likelihood of survival and reproduction, become more common in successive generations.

Factors such as predators, disease, and competition for resources can create selective pressures that favor certain phenotypes. Those organisms best adapted to their environment are more likely to reproduce, passing on their advantageous traits to their offspring. Over time, this can lead to populations evolving as these traits become more prevalent.

Selection Pressures

While individual organisms do not evolve, populations do through the gradual change in allele frequencies. It is worth noting that natural selection is not dependent on population size; rather, it is influenced by the specific selective pressures present in the environment and the genetic variability within the population.

Gene Migration

Gene migration, also known as gene flow, occurs when individuals or their gametes move from one population to another, resulting in the transfer of genetic material between populations. This movement can be the result of animals physically moving to new locations or pollen being transferred by wind or insects.

Gene migration is a critical factor in maintaining genetic diversity within a population, as it introduces new alleles that may be beneficial for the population's adaptation to changing environments. While population size can influence gene migration to some extent, geographical and behavioral barriers, along with ecological factors, play a more significant role.

Effects on Population Diversity

By homogenizing genetic differences, gene migration can counteract the effects of genetic drift and selection, especially in fragmented populations or those that are geographically isolated. High rates of gene flow can reduce inter-population genetic variation, while low rates may increase divergence, possibly leading to speciation.