BIOL 1307 Exam 3 Review – Step-by-Step Study Guidance

Q1. Graph each mode of natural selection: stabilizing selection, disruptive selection, and directional selection.

Background

Topic: Evolutionary Biology – Natural Selection

This question tests your understanding of the three main modes of natural selection and how they affect the distribution of phenotypes in a population over time.

Key Terms:

• Stabilizing selection: Selection that favors intermediate phenotypes and reduces variation.

• Disruptive selection: Selection that favors both extreme phenotypes over intermediates.

• Directional selection: Selection that favors one extreme phenotype, shifting the population mean.

Step-by-Step Guidance

1. Draw a bell-shaped curve to represent the original trait distribution in a population (x-axis: trait value, y-axis: frequency).

2. For stabilizing selection, show the evolved population with a narrower, taller curve centered at the original mean.

3. For disruptive selection, show the evolved population with two peaks at the extremes and a dip in the middle.

4. For directional selection, show the evolved population curve shifted toward one extreme.

Try sketching these graphs before checking examples!

Q2. Analyze frequency distributions of a trait in original and evolved populations to identify the type of selection occurring.

Background

Topic: Evolutionary Biology – Interpreting Selection Patterns

This question asks you to interpret graphical data showing trait distributions before and after selection to determine which mode of selection has occurred.

Key Concepts:

• Frequency distribution graphs (trait value vs. frequency)

• Patterns associated with stabilizing, disruptive, and directional selection

Step-by-Step Guidance

1. Examine the original and evolved population graphs for changes in the shape and position of the curve(s).

2. Look for narrowing (stabilizing), splitting into two peaks (disruptive), or shifting of the mean (directional).

3. Match the observed pattern to the definitions of the three selection modes.

Try matching the patterns before reviewing the answer!

Q3. List 5 conditions that lead to changes in allele frequency in a population and explain the difference between random and adaptive evolution.

Background

Topic: Population Genetics – Mechanisms of Evolution

This question tests your knowledge of the factors that can cause allele frequencies to change and the distinction between random and adaptive processes.

Key Terms:

• Allele frequency

• Genetic drift (random)

• Gene flow (random or adaptive)

• Mutation (random)

• Natural selection (adaptive)

• Non-random mating

Step-by-Step Guidance

List the five mechanisms: mutation, gene flow, genetic drift, natural selection, and non-random mating.

1. Briefly describe how each mechanism can alter allele frequencies.

2. Explain which mechanisms are random (e.g., mutation, genetic drift) and which are adaptive (e.g., natural selection).

3. Clarify the difference: random evolution changes allele frequencies by chance, while adaptive evolution increases fitness.

Try writing out your explanations before checking the answer!

Q4. List 4 sources of genetic variation and explain how each source contributes to genetic variation.

Background

Topic: Genetics – Sources of Variation

This question focuses on the mechanisms that generate genetic diversity within populations.

Key Terms:

• Mutation

• Gene flow

• Sexual reproduction (recombination, independent assortment, crossing over)

• Random fertilization

Step-by-Step Guidance

1. List four sources: mutation, gene flow, recombination (crossing over), and random fertilization.

2. For each, explain how it introduces new alleles or combinations into the gene pool.

3. Provide a brief example for each source.

Try to explain each source in your own words before checking the answer!

Q5. Given the genotypes in a population, calculate the frequency of each allele for a single locus with only 2 alleles.

Background

Topic: Population Genetics – Allele Frequency Calculation

This question tests your ability to calculate allele frequencies from genotype counts.

Key Formula:

$\text{Allele frequency of A} = \frac{2 \times \text{number of AA} + \text{number of Aa}}{2 \times \text{total individuals}}$

$\text{Allele frequency of a} = \frac{2 \times \text{number of aa} + \text{number of Aa}}{2 \times \text{total individuals}}$

Step-by-Step Guidance

1. Count the number of each genotype (e.g., AA, Aa, aa) in the population.

2. Calculate the total number of alleles (2 per individual).

3. Use the formulas above to find the frequency of each allele.

4. Check that the sum of allele frequencies equals 1.

Try calculating with sample numbers before checking the answer!

Q6. Use the Hardy-Weinberg principle to calculate expected frequency of alleles in a population where no change in allele frequency is occurring.

Background

Topic: Population Genetics – Hardy-Weinberg Equilibrium

This question tests your ability to apply the Hardy-Weinberg equation to predict genotype and allele frequencies under equilibrium conditions.

Key Formula:

$\text{p}^2 + 2\text{pq} + \text{q}^2 = 1$

$\text{p} + \text{q} = 1$

Step-by-Step Guidance

1. Identify the observed genotype frequencies or counts.

2. Calculate allele frequencies (p and q) using the formulas above.

3. Use the Hardy-Weinberg equation to calculate expected genotype frequencies.

4. Compare observed and expected frequencies to check for equilibrium.

Try working through the calculations before checking the answer!

Q7. Define and give examples of genetic drift, founder effect, and bottleneck effect.

Background

Topic: Evolutionary Mechanisms – Genetic Drift

This question tests your understanding of random changes in allele frequencies and specific scenarios where they occur.

Key Terms:

• Genetic drift: Random changes in allele frequencies, especially in small populations.

• Founder effect: Genetic drift that occurs when a few individuals start a new population.

• Bottleneck effect: Genetic drift following a drastic reduction in population size.

Step-by-Step Guidance

1. Define each term clearly.

2. Provide a real-world or hypothetical example for each effect.

3. Explain how each leads to changes in genetic diversity.

Try writing your own examples before checking the answer!