Figure 20.6 illustrates the effect of an ethanol-rich and an ethanol-free environment on the frequency of the Drosophila allele in four populations in a 50-generation laboratory experiment. Population 1 and population 2 were reared for 50 generations in a high-ethanol environment, while control 1 and control 2 populations were reared for 50 generations in a zero-ethanol environment. Describe the effect of each environment on the populations, and state any conclusions you can reach about the role of any of the evolutionary processes in producing these effects.

Key Concepts

Natural Selection

Natural selection is a fundamental mechanism of evolution where individuals with advantageous traits are more likely to survive and reproduce. In the context of the Drosophila populations, the ethanol-rich environment may favor alleles that confer tolerance to ethanol, leading to an increase in their frequency over generations. This process illustrates how environmental pressures can shape genetic variation within a population.

Genetic Drift

Genetic drift refers to random changes in allele frequencies within a population, particularly in small populations. In the Drosophila experiment, if the populations are small, random fluctuations could significantly impact the frequency of alleles, regardless of their adaptive value. This concept highlights the role of chance in evolution, especially in isolated or controlled environments.

Phenotypic Plasticity

Phenotypic plasticity is the ability of an organism to change its phenotype in response to environmental conditions. In the Drosophila study, the populations may exhibit different traits based on the ethanol levels, which could influence survival and reproduction. Understanding this concept is crucial for interpreting how environmental factors can lead to observable changes in populations over generations.