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Copy of Other Mechanisms of Evolution (5/2/2026)

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Last updated about 4 hours ago
30 Nsɛmmisa
Natural Selection or Something Else?

FUN FACT FRIDAY!

Natural selection or something else? Read the two scenarios below, then answer the questions in this section.

Other Mechanisms of Evolution
Exit Ticket
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Scenario #1: A bird eats green beetles because they stand out on a tree.

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1.

What is happening to the number of green beetles over time (from left to right)?

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Scenario #2: A person steps on a population of beetles at random.

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5.

What is happening to the number of green beetles over time (from left to right)?

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We know that Natural Selection (or "Survival of the Fittest") tells us that organisms with the better traits are the ones that survive and reproduce. This helps to drive Evolution (the change in heritable traits over time). One of the main principles of natural selection is that Nature Chooses which individuals will survive.

However, Natural Selection is not the only mechanism that drives evolution. Today, you will learn about four other mechanisms of evolution.

Sometimes unpredictable events happen in nature, and populations are randomly affected. We call this Genetic Drift: when allele frequencies in populations are affected by random chance, not necessarily because they have better traits. With genetic drift, random luck decides which organisms survive.

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9.

What is the difference between Natural Selection and Genetic Drift?

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10.

Natural selection is the ONLY driving force behind evolution.

There are two examples of Genetic Drift: the Bottleneck Effect and the Founder Effect. The first type we will look at is the Bottleneck Effect. This is usually driven by very rapid changes in the environment.

In the Bottleneck Effect, an event will suddenly drastically reduce the size of a population, changing the allele frequency at random. Examples include volcanic eruptions, earthquakes, floods, and hunting.

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The next type of genetic drift is called the Founder Effect.

In the Founder Effect, a small population is separated from the original population, then forms a new colony of individuals.

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15.

Which alleles were present in the original population?

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The third mechanism of evolution is called gene flow. This is caused by movement of individuals into or out of a population. As new alleles enter or exit the population, frequencies of genes within the gene pool (all of the alleles present in the population) change.

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18.

If Population A and Population B were to combine, what would happen to the variation within the gene pool?

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The fourth mechanism of evolution is mutations. Remember that mutations are changes in the nitrogen base sequence of DNA, which then change amino acid sequences that build proteins. When mutations occur, new phenotypes are added to the gene pool. These mutations can either be good or bad, depending on the environment.

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20.

What happens to genetic variation as a result of Mutations?

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The last mechanism of evolution is Non-Random Mating. In short, organisms have at least some kind of preference in who they choose to mate with. Think about it: would you date just any stranger? Probably not! Organisms in the animal kingdom are the same way.

As a result of Non-Random Mating, certain genotypes or phenotypes become more common in the population than others.

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23.

Suppose the brown females in a particular species of bird prefer to mate with bright red male birds over dark red male birds. What will happen to the dark red allele frequency over time?

To summarize, there are five mechanisms for evolution: Natural Selection, Genetic Drift, Gene Flow, Mutations, and Non-Random Mating.

Natural selection is based on the principle that organisms with better traits are the ones who survive and reproduce.

Genetic Drift, on the other hand, is based on random chance and does not take into consideration which traits are "better". The two examples of Genetic Drift are the Bottleneck Effect (sudden decease in the population) and the Founder Effect (small population is isolated and forms a new colony).

Gene flow is the movement or exchange of alleles between different populations.

Mutations can be good or bad, and increase the variation in a population by introducing new alleles.

Non-Random Mating suggests that certain genotypes or phenotypes are more preferable than others, and organisms choose who to mate with.

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24.

Match each mechanism of evolution with its definition.

Draggable itemarrow_right_altCorresponding Item

Non-Random Mating

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Nature chooses; organisms with better traits survive and reproduce.

Natural Selection

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Sudden random decrease in population that also decreases variation.

Gene Flow

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When a small population is isolated from the larger population, then forms a new colony.

Bottleneck Effect

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Movement or exchange of alleles into or out of a population.

Founder Effect

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Random change in DNA that creates new alleles in the population.

Mutations

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When certain characteristics are preferred over others in a population.

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25.

The Afrikaner population in South Africa came from a few colonists that settled there hundreds of years ago.

Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease. Scientists believe this is because the original colonists who settled in this new colony carried the gene with high frequency.

Which mechanism of evolution explains the high frequency of Huntington's disease in the population?

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26.

In a forest, beetles with flat legs stay on the ground, while beetles with hooks can climb trees. A certain predator eats beetles close to the ground. Over time, the frequency of beetles with hooks increases in the population, while the frequency of beetles with flat legs decreases.

Which mechanism of evolution explains the change in allele frequency in the population?

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27.

In Antarctica, there used to be 4 different allele variations of seals: those with brown fur, white fur, gray fur, and black fur. Seals with gray fur and black fur were hunted in the 1800s in order to make dark fur coats.

Which mechanism of evolution explains the change in allele frequency in the population?

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28.

Sara is studying flies inside of her genetics lab. In week 1, she records that 75% of the population has red eyes and 25% of the population has white eyes. After 3 weeks, she notices that 50% have red eyes, 25% have white eyes, and 25% have orange eyes.

If no other flies have entered or left the population, which mechanism of evolution explains this change in allele frequency?

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29.

The Rocky Mountains are home to two populations of deer. In the Western deer population, 100% of the population has light brown fur. In the Eastern deer population, 100% have dark brown fur. In 1906, a clearing was created through the mountain range, allowing the two populations to interact for the first time in centuries. We now observe that in the Eastern deer population, 80% have dark brown fur, and 20% have light brown fur.

Which mechanism of evolution explains the change in allele frequency in the population?

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30.

In the Kampong Gardens of Florida, 50% of male peacocks have 250 eyespots and 50% have 100 eyespots on their feathers. After 5 years, researchers have noticed that 80% of males have 250 eyespots, and only 20% have 100 eyespots.

Which mechanism of evolution explains the change in allele frequency in the population?

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2.

What is happening to the number of brown beetles over time (from left to right)?

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3.

Which variation of beetle would be considered the most "fit"?

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4.

Would this change within the beetle population be considered an example of Natural Selection? (Did nature choose what the better trait was?)

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6.

Which allele had more survivors?

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7.

Which variation of beetle would be considered the most "fit"?

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8.

Would this change within the beetle population be considered an example of Natural Selection? (Did nature choose what the better trait was?)

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11.

Which alleles had the highest frequency in the original population?

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12.

Which alleles had the highest frequency after the bottleneck event?

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13.

What happened to the variation after the bottleneck event?

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14.

Suppose a disease spreads in the new population. What would happen to the population if only the green iguanas had a gene to protect against it?

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16.

Which alleles were present in the new population?

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17.

What happens to genetic variation as a result of the Founder Effect?

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19.

What is meant by the term "gene pool"?

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21.

Suppose the mutation that created the orange iguana prevents them from camouflaging in the forest from predators.

Is the mutation good or bad, and what will happen to the population of orange iguanas over time?

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22.

Suppose the mutation that created the orange iguana allows them to produce toxins from their skin to protect themselves against predators.

Is the mutation good or bad, and what will happen to the population of orange iguanas over time?