Question

1. Explain all of the terms: gene, allele, population, gene pool, microevolution, allele frequency, genotype, phenotype, homozygous, heterozygous, dominant, recessive, and genotype frequency.

2. Explain the two equations and all the variables involved in Hardy-Weinberg (HW) equilibrium.

3. Explain the five assumptions under which HW operates.

4. Explain the importance of HW (even though it doesn't happen in real life).

5. Explain the five primary sources of variation: two adaptive (NS and non-random
mating) and three non-adaptive (genetic drift, gene flow, and mutations).

6. Explain and be able to identify examples of the three positive and negative patterns of natural selection.

7. Explain and be able to identify examples of balancing selection and heterozygote advantage.

8. Explain and be able to identify examples of the bottleneck effect and founder effect.

9. Explain and be able to identify examples of assertive mating and inter- and intra-sexual selection.

Answer 1

1. Definitions:

- Gene: DNA segment carrying trait information.

- Allele: Variant form of a gene.

- Population: Group of interbreeding individuals in an area.

- Gene pool: Complete set of genes in a population.

- Microevolution: Small-scale genetic changes in a population.

- Allele frequency: Proportion of an allele in the gene pool.

- Genotype: Combination of alleles in an individual.

- Phenotype: Observable traits from genotype.

- Homozygous: Having identical alleles for a gene.

- Heterozygous: Having different alleles for a gene.

- Dominant: Trait expressed in the presence of another allele.

- Recessive: Trait expressed only in the absence of a dominant allele.

- Genotype frequency: Proportion of individuals with a specific genotype.

2. Hardy-Weinberg Equilibrium (HW):

- p^2 + 2pq + q^2 = 1 (allele frequency equation)

- p + q = 1 (sum of allele frequencies)

3. Assumptions of HW equilibrium:

- Random mating

- Large population size

- No gene flow

- No mutations

- No natural selection

4. Importance of HW equilibrium:

Though idealized, it serves as a reference for studying evolution and detecting deviations from expected frequencies.

5. Sources of variation:

- Adaptive: Natural selection and non-random mating.

- Non-adaptive: Genetic drift, gene flow, and mutations.

6. Positive patterns of natural selection:

- Directional: One extreme phenotype favored.

- Stabilizing: Intermediate phenotype favored.

- Disruptive: Extreme phenotypes favored.

7. Balancing selection and heterozygote advantage:

- Balancing: Multiple alleles maintained (e.g., sickle cell anemia).

- Heterozygote advantage: Higher fitness for heterozygous individuals (e.g., sickle cell trait).

8. Bottleneck effect and founder effect:

- Bottleneck: Population size drastically reduced.

- Founder: Small group establishes a new population.

9. Assertive mating and inter- / intra-sexual selection:

- Assertive mating: Selection based on similar traits (e.g., selective breeding).

- Intersexual selection: Mating preference based on traits (e.g., peacock tails).

- Intrasexual selection: Competition within a sex for mating access (e.g., antler battles).

Answer 2

1.
- **Gene:** A gene is a segment of DNA that carries instructions for a specific trait or function in an organism's genetic code.

- **Allele:** Alleles are different versions of a gene, each with a unique DNA sequence, which can lead to variations in traits.

- **Population:** A population is a group of interbreeding individuals of the same species in a defined geographic area.

- **Gene Pool:** The gene pool is the total collection of genes and alleles present in a population.

- **Microevolution:** Microevolution refers to small-scale genetic changes that occur within a population over generations, leading to changes in allele frequencies.

- **Allele Frequency:** Allele frequency is the proportion of a specific allele in a population's gene pool.

- **Genotype:** Genotype represents the genetic makeup of an individual, determined by the combination of alleles they possess.

- **Phenotype:** Phenotype is the observable physical or biochemical expression of an organism's genotype.

- **Homozygous:** Homozygous individuals carry two identical alleles for a particular gene (e.g., AA or aa).

- **Heterozygous:** Heterozygous individuals have two different alleles for a particular gene (e.g., Aa).

- **Dominant:** A dominant allele masks the expression of a recessive allele when present in a heterozygous genotype.

- **Recessive:** A recessive allele is expressed only when an individual is homozygous for it (aa).

- **Genotype Frequency:** Genotype frequency is the proportion of individuals in a population with a specific genotype.

2. The Hardy-Weinberg equilibrium equations:
- **p² + 2pq + q² = 1** (p² represents the frequency of homozygous dominant individuals, 2pq represents the frequency of heterozygous individuals, and q² represents the frequency of homozygous recessive individuals)
- **p + q = 1** (p represents the frequency of the dominant allele, and q represents the frequency of the recessive allele).

3. The five assumptions under which Hardy-Weinberg operates:
- **No mutation:** Gene mutations do not occur.
- **No migration:** There is no gene flow in or out of the population.
- **Large population:** The population is sufficiently large to prevent genetic drift.
- **Random mating:** Mating occurs randomly without preference for specific genotypes.
- **No natural selection:** No individuals have a survival or reproductive advantage based on their genotype.

4. The importance of Hardy-Weinberg equilibrium lies in its role as a null hypothesis, a baseline for understanding how evolutionary forces like mutation, migration, genetic drift, natural selection, and non-random mating shape populations. Deviations from HW provide insights into these forces' impact on genetic diversity and adaptation.

5.
- **Adaptive Variation:** Natural selection (NS) and non-random mating can lead to adaptive variation, favoring alleles that increase fitness in specific environments.

- **Non-Adaptive Variation:** Genetic drift, gene flow, and mutations contribute to non-adaptive variation, which doesn't necessarily confer a fitness advantage.

6.
- **Positive Patterns of Natural Selection:** Directional selection (favoring one extreme phenotype), stabilizing selection (favoring intermediate phenotypes), and disruptive selection (favoring extreme phenotypes).

- **Negative Patterns of Natural Selection:** Purifying selection (elimination of deleterious alleles) and balancing selection (maintaining multiple alleles).

7.
- **Balancing Selection:** Balancing selection occurs when heterozygotes have a fitness advantage over homozygotes, maintaining genetic diversity. Example: Sickle cell anemia and resistance to malaria.

8.
- **Bottleneck Effect:** A population undergoes a drastic size reduction, leading to limited genetic diversity. Example: The northern elephant seal population.

- **Founder Effect:** A small group establishes a new population, carrying a subset of the original gene pool, leading to reduced genetic diversity. Example: The Amish population.

9.
- **Assortative Mating:** Individuals prefer mates with similar traits. Example: People with similar educational backgrounds marrying.

- **Intersexual Selection:** One sex chooses mates based on specific traits. Example: Peahens choosing peacocks with impressive tail feathers.

- **Intrasexual Selection:** Members of one sex compete for access to mates. Example: Male deer competing for mating rights with antler size.