Biology: Conservation Genetics: Bottlenecks and Founder Effects Worksheet

Question 1

Define a population bottleneck in your own words, and explain why it can reduce genetic diversity even if the population later grows larger.

Accepted Answer

A population bottleneck happens when a population is sharply reduced in size by an event such as disease, hunting, habitat loss, or a natural disaster. Genetic diversity can be reduced because the surviving individuals may carry only a small sample of the original alleles, and later population growth mostly copies the genes of those few survivors.

Question 2

Define the founder effect and give one realistic conservation example.

Accepted Answer

The founder effect occurs when a new population is started by a small number of individuals from a larger population. For example, if a few island birds colonize a new island, their descendants may have allele frequencies that differ from the original mainland population because the founders carried only part of the mainland gene pool.

Question 3

A population of 1,000 prairie chickens has 120 copies of allele A and 1,880 copies of allele a at a gene with two alleles. What is the frequency of allele A? Assume each bird has two copies of the gene.

Accepted Answer

There are 2,000 total allele copies because 1,000 diploid birds each have 2 copies. The frequency of allele A is 120 divided by 2,000, which equals 0.06, or 6%.

Question 4

After a severe storm, only 20 of the 1,000 prairie chickens survive. In the survivors, there are 10 copies of allele A and 30 copies of allele a. What is the new frequency of allele A, and what does this show about genetic drift?

Accepted Answer

There are 40 total allele copies in the 20 surviving birds. The frequency of allele A is 10 divided by 40, which equals 0.25, or 25%. This shows that genetic drift can strongly change allele frequencies by chance, especially when the population becomes very small.

Question 5

Explain how a population bottleneck differs from natural selection.

Accepted Answer

A bottleneck is usually a chance event that randomly removes many individuals from a population, although some survival may be related to traits depending on the event. Natural selection occurs when individuals with certain heritable traits survive or reproduce more successfully because those traits give an advantage in a specific environment.

Question 6

A wildlife biologist samples two populations of the same fish species. Population X has 18 different alleles across several genetic markers. Population Y has 6 different alleles at the same markers. Which population likely has more genetic diversity, and why is that important for conservation?

Accepted Answer

Population X likely has more genetic diversity because it has more different alleles across the genetic markers. Higher genetic diversity is important because it can give a population more ability to adapt to disease, climate change, and other environmental pressures.

Question 7

Look at a diagram showing allele frequencies before and after a bottleneck. The original population has red, blue, green, and yellow allele types. After the bottleneck, only red and blue remain. Explain what happened to the green and yellow alleles and why this matters.

Accepted Answer

The green and yellow alleles were lost when individuals carrying them did not survive or reproduce after the bottleneck. This matters because lost alleles reduce genetic diversity, and the population may have fewer options for adapting to future environmental changes.

Question 8

A small group of 8 lizards is moved to a predator-free island to start a new population. By chance, none of the founders carry an allele that was present in 15% of the mainland population. Identify the evolutionary process and explain the result.

Accepted Answer

This is an example of the founder effect. The island population begins without that allele because the founding lizards did not carry it, so the allele frequency on the island is 0% even though it was present in the mainland population.

Question 9

Why can inbreeding become a serious problem after a bottleneck or founder event?

Accepted Answer

Inbreeding can become a serious problem because a small population has fewer unrelated mates. Close relatives are more likely to share the same harmful recessive alleles, so offspring have a higher chance of inheriting two copies of those alleles and showing genetic disorders or reduced fitness.

Question 10

A conservation team wants to increase genetic diversity in an isolated wolf population. They are considering moving a few wolves from a nearby population into the isolated group. What is this strategy called, and what is one possible benefit and one possible risk?

Accepted Answer

This strategy is often called genetic rescue. A possible benefit is that new wolves can introduce new alleles and reduce inbreeding. A possible risk is that the introduced wolves may bring diseases or genes that are poorly adapted to the local environment.

Question 11

A graph shows population size over time for an endangered seal species. The population drops from 50,000 to 200 individuals in the 1890s and then rises to 30,000 by the present. Predict whether the present population is likely to have high or low genetic diversity compared with the original population, and explain why.

Accepted Answer

The present population is likely to have low genetic diversity compared with the original population. Even though the number of seals recovered, most present-day seals descended from the small group of 200 survivors, so many original alleles may have been lost during the bottleneck.

Question 12

In a captive breeding program, why should managers avoid choosing breeding pairs only from animals that look healthy?

Accepted Answer

Managers should avoid relying only on appearance because animals that look healthy may still be closely related or may carry the same harmful recessive alleles. Genetic testing and pedigree records help managers choose pairs that preserve more genetic diversity and reduce inbreeding.

Question 13

A plant population has three alleles at a flower-color gene: R, W, and P. Before a fire, allele frequencies are R = 0.50, W = 0.30, and P = 0.20. After the fire, the surviving plants have allele frequencies R = 0.80, W = 0.20, and P = 0.00. Which allele was lost, and what type of event likely caused this pattern?

Accepted Answer

The P allele was lost because its frequency changed to 0.00. This pattern likely resulted from a population bottleneck if the fire sharply reduced the population and the surviving plants happened not to carry the P allele.

Question 14

Explain why small populations are more affected by genetic drift than large populations.

Accepted Answer

Small populations are more affected by genetic drift because random changes have a larger effect when there are fewer individuals and fewer allele copies. In a large population, chance events usually affect a smaller fraction of the total gene pool.

Question 15

A conservation plan proposes creating three separate reserves for an endangered mammal, each started with 10 individuals. Another plan proposes one connected reserve where all 30 individuals can interbreed. Based on conservation genetics, which plan may better preserve genetic diversity over time, and why?

Accepted Answer

The connected reserve may better preserve genetic diversity over time because all 30 individuals can interbreed, which increases gene flow and reduces the chance that each small group will lose different alleles by genetic drift. Separate reserves can be useful for reducing disease or disaster risk, but very small isolated groups are more vulnerable to inbreeding and allele loss.

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Biology: Conservation Genetics: Bottlenecks and Founder Effects

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