Study Guide: Evolution of Populations (Ch. 21)

Q1. Be able to explain genetic variation.

Background

Topic: Genetic Variation in Populations

This question tests your understanding of what genetic variation is and why it is important for evolution and population genetics.

Key Terms:

• Genetic Variation: Differences in DNA sequences among individuals in a population.

• Allele: Different forms of a gene found at the same locus.

Step-by-Step Guidance

1. Start by defining genetic variation in your own words. Consider how it relates to differences in traits among individuals.

2. Think about why genetic variation is necessary for evolution to occur. What role does it play in natural selection?

3. Consider examples of genetic variation, such as differences in eye color, blood type, or resistance to disease.

Try explaining this concept in your own words before checking the answer!

Q2. Know the sources of genetic variation.

Background

Topic: Sources of Genetic Variation

This question is about identifying and understanding the mechanisms that create genetic diversity within populations.

Key Terms:

• Mutation: A change in the DNA sequence.

• Recombination: The reshuffling of alleles during meiosis (crossing over and independent assortment).

• Gene Flow: Movement of alleles between populations.

Step-by-Step Guidance

1. List the main sources of genetic variation in populations.

2. For each source, briefly describe how it introduces new genetic combinations or alleles.

3. Think about which sources create entirely new alleles and which shuffle existing alleles.

Try listing and describing the sources before checking the answer!

Q3. Know phenotype vs. genotype.

Background

Topic: Phenotype and Genotype

This question tests your ability to distinguish between an organism's genetic makeup and its observable traits.

Key Terms:

• Genotype: The genetic constitution of an organism (the alleles it carries).

• Phenotype: The observable physical or physiological traits of an organism, determined by its genotype and environment.

Step-by-Step Guidance

1. Define genotype and phenotype in your own words.

2. Think of examples where the genotype determines the phenotype (e.g., flower color in pea plants).

3. Consider how the environment can influence phenotype, even with the same genotype.

Try explaining the difference before checking the answer!

Q4. Understand where mutations occur and which mutations can be passed on to the next generation.

Background

Topic: Mutations and Heritability

This question is about the types of cells where mutations can occur and which of those mutations are heritable.

Key Terms:

• Somatic Cells: All body cells except gametes; mutations here are not passed to offspring.

• Germ Cells: Cells that give rise to gametes (sperm and eggs); mutations here can be inherited.

Step-by-Step Guidance

1. Recall the difference between somatic and germ cells.

2. Identify where mutations must occur to be passed to the next generation.

3. Think about why only certain mutations are heritable.

Try identifying which mutations are heritable before checking the answer!

Q5. Define natural selection.

Background

Topic: Natural Selection

This question tests your understanding of the mechanism by which certain traits become more common in a population over time.

Key Terms:

• Natural Selection: The process by which individuals with advantageous traits survive and reproduce more successfully.

• Fitness: The ability to survive and reproduce in a given environment.

Step-by-Step Guidance

1. Write a concise definition of natural selection.

2. Include the role of variation, differential survival, and reproduction.

3. Think of an example where natural selection might occur (e.g., antibiotic resistance in bacteria).

Try defining natural selection before checking the answer!

Q6. Know the non-adaptive mechanisms of evolution: genetic drift, founder effect, bottleneck effect, migration (gene flow), and mutation.

Background

Topic: Non-Adaptive Evolutionary Mechanisms

This question is about understanding evolutionary changes that are not due to natural selection.

Key Terms:

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

• Founder Effect: When a new population is started by a small number of individuals, leading to reduced genetic variation.

• Bottleneck Effect: A sharp reduction in population size due to a random event, reducing genetic diversity.

• Gene Flow: Movement of alleles between populations (migration).

• Mutation: Random changes in DNA that introduce new alleles.

Step-by-Step Guidance

1. List each mechanism and provide a brief definition.

2. Think of an example for each mechanism.

3. Consider how these mechanisms differ from natural selection.

Try describing each mechanism before checking the answer!

Q7. Understand how natural selection can influence the frequency of phenotypes in a population: directional selection, disruptive selection, and stabilizing selection.

Background

Topic: Types of Selection

This question is about the different patterns by which natural selection can shift phenotype frequencies in a population.

Key Terms:

• Directional Selection: Favors one extreme phenotype.

• Disruptive Selection: Favors both extreme phenotypes over intermediate forms.

• Stabilizing Selection: Favors intermediate phenotypes and reduces variation.

Step-by-Step Guidance

1. Define each type of selection.

2. Draw or imagine a graph showing how phenotype frequencies change under each type.

3. Think of an example for each selection type.

Try explaining each selection type before checking the answer!

Q8. Understand how natural selection can change the frequencies of alleles: positive selection, negative selection, and balancing selection.

Background

Topic: Selection and Allele Frequencies

This question is about how different forms of selection affect allele frequencies in a population.

Key Terms:

• Positive Selection: Increases the frequency of beneficial alleles.

• Negative Selection: Decreases the frequency of harmful alleles.

• Balancing Selection: Maintains multiple alleles in the population.

Step-by-Step Guidance

1. Define each type of selection in terms of allele frequency changes.

2. Think of examples where each type might occur (e.g., sickle cell allele and malaria for balancing selection).

3. Consider how these processes maintain or reduce genetic diversity.

Try describing each selection type before checking the answer!

Q9. Be able to explain frequency-dependent selection.

Background

Topic: Frequency-Dependent Selection

This question is about a special case where the fitness of a phenotype depends on its frequency in the population.

Key Terms:

• Frequency-Dependent Selection: The fitness of a phenotype changes depending on how common or rare it is.

Step-by-Step Guidance

1. Define frequency-dependent selection.

2. Think of an example, such as predator-prey interactions or host-parasite dynamics.

3. Consider how this type of selection can maintain genetic diversity.

Try explaining this concept before checking the answer!

Q10. Know the difference between natural selection and sexual selection.

Background

Topic: Natural vs. Sexual Selection

This question is about distinguishing between selection for survival and selection for mating success.

Key Terms:

• Natural Selection: Selection for traits that improve survival and reproduction.

• Sexual Selection: Selection for traits that increase mating success, even if they do not improve survival.

Step-by-Step Guidance

1. Define both natural selection and sexual selection.

2. Think of examples where sexual selection leads to traits that might not be favored by natural selection (e.g., peacock tails).

3. Consider how these two forms of selection can act together or in opposition.

Try explaining the difference before checking the answer!

Q11. Know the difference between intrasexual selection and intersexual selection.

Background

Topic: Types of Sexual Selection

This question is about the two main mechanisms by which sexual selection operates.

Key Terms:

• Intrasexual Selection: Competition among individuals of the same sex (usually males) for mates.

• Intersexual Selection: Mate choice, where one sex (usually females) selects mates based on certain traits.

Step-by-Step Guidance

1. Define intrasexual and intersexual selection.

2. Think of examples for each (e.g., male-male combat vs. female choice).

3. Consider how these processes can lead to different evolutionary outcomes.

Try explaining the difference before checking the answer!

Q12. Know the costs and benefits of sexual selection.

Background

Topic: Sexual Selection Trade-Offs

This question is about understanding why sexually selected traits can be both advantageous and costly.

Key Terms:

• Costs: Increased risk of predation, energy expenditure, or reduced survival.

• Benefits: Increased mating success and reproductive output.

Step-by-Step Guidance

1. List potential costs of sexual selection (e.g., bright colors attracting predators).

2. List potential benefits (e.g., attracting more mates).

3. Think of examples where the trade-off is evident.

Try listing costs and benefits before checking the answer!

Q13. Know which sex is more favored by sexual selection vs. the sex that is more influenced by natural selection.

Background

Topic: Sex Differences in Selection

This question is about understanding how sexual and natural selection can act differently on males and females.

Key Terms:

• Sexual Selection: Often acts more strongly on males, leading to elaborate traits.

• Natural Selection: Can act more strongly on females, especially regarding survival and parental investment.

Step-by-Step Guidance

1. Consider why males often compete for mates and females are choosier.

2. Think about how sexual selection can lead to differences in appearance or behavior between sexes.

3. Reflect on how natural selection might favor traits that increase survival, especially in females.

Try explaining these differences before checking the answer!