Question

In which of the following pairs do both evolutionary processes introduce new genetic variation into a population? a. natural selection and genetic drift b. mutation and gene flow C. natural selection and gene flow d. gene flow and genetic drift

Short answer

The correct pair of evolutionary processes that introduce new genetic variation into a population is b. mutation and gene flow. Mutation creates new genetic variants, and gene flow introduces new alleles from different populations, increasing genetic variation.

Step-by-step solution

Understand each evolutionary process

Before selecting the correct pair, the student must have a basic understanding of each evolutionary process mentioned in the options. 1. Natural Selection: It's a process where individuals with more favorable traits have a higher chance of survival and reproduction. This leads to an increase in the frequency of those traits within the population. Overall, natural selection does not create new genetic variants but selects certain traits that already exist in a population. 2. Genetic Drift: It's a random change in allele frequency within a population due to chance events. Genetic drift can lead to the loss of genetic variation within a population, but it does not create new genetic variation. 3. Mutation: This is a random change in the DNA sequence, which can lead to the formation of new alleles or traits. Mutation is the primary source of new genetic variation in populations. 4. Gene Flow: This process occurs when alleles from one population are transferred and introduced to another population. Gene flow can increase the genetic variation within a population by introducing new alleles from a different population.

Identify the correct pair

Now that each evolutionary process has been defined, it's time to identify which pairs of processes introduce new genetic variation into a population. a. Natural Selection and Genetic Drift: Neither of these processes create new genetic variation, they only change the frequency or loss of existing alleles within a population. b. Mutation and Gene Flow: Mutation creates new genetic variants, and gene flow introduces new alleles from different populations, increasing genetic variation. c. Natural Selection and Gene Flow: Natural selection does not create new genetic variation, while gene flow does introduce new alleles from different populations. However, this pair does not have both processes introducing new genetic variants. d. Gene Flow and Genetic Drift: Gene flow introduces new alleles from different populations, while genetic drift does not create new genetic variation. Thus, the correct answer is: b. mutation and gene flow

Key concepts

Natural Selection

Natural selection is often mistakenly thought to generate new genetic traits, but its power lies in amplifying or reducing the frequency of already existing traits that influence an organism's fitness. Imagine a family of beetles where some are green, and some are brown. If the environment is full of green plants, the green beetles might be less visible to predators. Over generations, because of this camouflage, more green beetles survive to reproduce than brown ones. This is natural selection in action, favoring green beetles; however, notice that it didn't create the green trait – it already existed.

It is vital to understand that natural selection can lead to evolution only if the traits being selected for have a heritable basis. Helpful adaptations may eventually become more common in the population, leading to evolutionary change over time.

Genetic Drift

Genetic drift might seem less glamorous next to natural selection, but it plays a crucial role in the evolution of populations, particularly small ones. Unlike natural selection, genetic drift is about random chances. Suppose we have a jar of 50 red and 50 blue marbles (genes), and we randomly remove 50 marbles. If by chance more blue marbles are removed, the jar will now have a higher proportion of red marbles. In a small population, chance events like deaths from a natural disaster can change the genetic makeup in a similar way, regardless of the organisms' traits.

However, genetic drift does not introduce new genetic variants; it only changes the frequencies of existing alleles. Over time, genetic drift can significantly impact a population's genetic diversity, leading to differences from the original gene pool, or even the accidental loss of alleles from a population.

Mutation

If natural selection and genetic drift work with the genetic material on hand, mutations are like the unexpected delivery of new building blocks. These random changes in the DNA sequence can occur during DNA replication or because of environmental factors like radiation. Mutations can result in new alleles, which might produce new traits that can be beneficial, neutral, or deleterious.

For example, a mutation might cause a plant to grow a slightly different leaf shape that could be better at capturing sunlight. If this new leaf shape is advantageous, natural selection might increase its frequency in the population. Without mutations introducing these new genetic options, the potential for evolution would be severely limited, as there would be no new material for natural selection to act upon.

Gene Flow

The concept of gene flow might seem straightforward, but its implications for genetic variation are profound. When individuals from one population migrate and breed with another population, they introduce their unique alleles into the local gene pool. This mixing of gene pools can add diversity to a population that may otherwise be quite uniform.

Consider a population of flowers on one side of a river that are all red, while on the other side, they're all white. If pollinators like bees bring pollen from the white flowers to the red ones, the offspring may exhibit a variety of colors not previously seen in either population. This new genetic variation is a direct result of gene flow. It's a process that can work in tandem with mutation, providing a mechanism for new genetic variations to spread across populations.