Comprehensive Study Guide for Microevolution and Macroevolution
Genetic Diversity: Fundamentals and Importance
Definition of Genetic Diversity: This refers to the genetic variation found among individuals belonging to the same species. It is characterized by individuals possessing different alleles, traits, and unique combinations of genes.
Importance of Genetic Diversity: * Evolutionary Potential: Populations possessing higher levels of genetic diversity are more likely to adapt to environmental changes. * Disease Resistance: Genetic variation ensures that some individuals may have genes that allow them to survive a disease outbreak, preventing total population collapse. * Antibiotic Resistance: In microorganisms, genetic diversity allows certain bacteria to survive exposure to antibiotics and subsequently reproduce.
Microevolution vs. Macroevolution
Macroevolution: * Defined as large-scale evolutionary change. * Occurs over long periods of time. * Results in the formation of new species (known as speciation).
Microevolution: * Defined as small-scale evolutionary change occurring within a population. * Caused by a change in allele frequencies over time. * Example: Bacteria developing antibiotic resistance or changes in the frequency of beetle colors within a population.
Relationship: Given enough time, microevolutionary changes can accumulate and lead to macroevolution (speciation).
Populations and Mechanisms of Microevolutionary Change
Definition of a Population: A group of individuals of the same species that live in the same area at the same time and possess the potential to interbreed.
Mechanisms of Microevolutionary Change: * Mutation: A change in the organism's DNA. It is the primary way new alleles are created and is random with respect to fitness. * Gene Flow: The movement of alleles between different populations. This occurs through migration and is random with respect to fitness. * Genetic Drift: A shift in the allele frequencies within a population caused by random deaths and mating. This is random with respect to fitness and is most pronounced in small populations. * Natural Selection: Occurs when individuals with certain traits tend to survive and produce more offspring than those without the traits. This is non-random with respect to fitness. * Sexual Selection: Occurs when members of one sex choose mates based on specific traits or behaviors. This is non-random with respect to fitness.
Genetic Mutations and Inheritence
Generation of New Alleles: Mutations are the primary source of new genetic variation in a population because they permanently change the DNA sequence.
Somatic vs. Germ (Reproductive) Cells: * Somatic Mutations: These occur in body cells and are generally not passed on to the next generation. * Germ Cell Mutations: Only mutations occurring in reproductive or germ cells can be inherited by offspring.
Mutation Effects: Most mutations are deleterious (harmful), though some can be beneficial or neutral.
Genetic Drift: Bottlenecks and Founder Effects
Genetic Drift: The random change in allele frequencies, which has a larger impact on small populations.
Founder Effect: This occurs when a small group of individuals breaks away from a larger population to establish a new, isolated population.
Genetic Bottleneck: This occurs when a population suddenly shrinks in size (e.g., due to a natural disaster). This leads to a significant loss of genetic variation because the few survivors only carry a fraction of the original population's alleles.
Negative Impact of Allele Loss: Reducing genetic diversity makes populations less capable of adapting to diseases, environmental shifts, or other challenges.
Fitness, Adaptation, and Selection
Biological Fitness: Defined as an organism's ability to survive and reproduce more offspring compared to other individuals in the same species. It is measured by the number of offspring produced.
Adaptation: A heritable trait that assists an organism in surviving and reproducing more effectively in its specific environment.
Natural Selection: This process involves organisms with helpful traits surviving and reproducing at higher rates than those without those traits.
Artificial Selection: Unlike natural selection, this is driven by humans who choose which plants or animals reproduce based on desired traits.
Survival vs. Reproduction: Natural selection is not solely about survival; an organism must survive long enough to reproduce and pass its traits to the next generation.
Selective Pressures: These are environmental factors that make survival difficult, such as predators, weather, and disease. Natural selection acts on populations in response to these pressures, and over time, the resulting helpful traits become adaptations.
Case Studies in Natural Selection
Peppered Moths: During the Industrial Revolution, trees became darkened by soot. Darker-colored moths blended in better and survived more frequently, causing the population to become predominantly dark.
Antibiotic Resistance: Some bacteria possess mutations that make them resistant to antibiotics. When antibiotics kill the normal bacteria, the resistant ones survive and reproduce.
Disease Resistance: Some humans naturally possess genes that help them resist diseases like HIV or the Bubonic Plague. These individuals are more likely to survive and pass these resistance genes to offspring.
Galapagos Finches: Finches with different beak shapes survived better depending on the food sources available on different islands. Over time, specific beak types became common in specific environments.
Sickle Cell Anemia: Individuals with the sickle cell trait have increased resistance to malaria. Consequently, the trait is very common in geographic areas where malaria is prevalent.
Evolutionary Patterns: Coevolution and Convergent Evolution
Coevolution: Occurs when two species influence each other’s evolution over time. * Predators and Prey (Cheetah and Antelope): As cheetahs evolved to run faster to catch prey, antelopes evolved to run faster to escape them. * Flowers and Pollinators: Flowers evolved specific colors, smells, and shapes to attract pollinators, while pollinators evolved specific body parts to collect nectar and spread pollen. * Newts and Garter Snakes: Rough-skinned newts evolved powerful toxins for protection, while garter snakes evolved a resistance to those toxins so they could continue to eat the newts.
Convergent Evolution: Occurs when unrelated species evolve similar traits independently because they live in similar environments and face similar selective pressures.
Sexual Selection and Dimorphism
Sexual Selection: This happens when organisms choose mates based on specific traits or behaviors.
Sexual Dimorphism: Sexual selection leads to sexual dimorphism, which refers to physical differences (size, color, ornamentation) between males and females of the same species.
The Trade-off of Traits: Females do not always choose males with traits that are best for survival. For example, bright colors may attract predators and make survival harder, but they are retained because they help the male attract a mate.
Speciation and the Biological Species Concept
Definition of a Species (Biological Species Concept): A group of organisms that can interbreed to produce viable offspring and are reproductively isolated from other such groups.
Reproductive Isolation: This occurs when two populations cannot interbreed or exchange genes. It is a critical component of defining a species because once reproduction stops between groups, they are considered separate species.
Five Steps of Speciation: 1. A population becomes separated into different groups. 2. The groups stop interbreeding. 3. Different mutations, natural selection, genetic drift, and gene flow affect the groups independently. 4. The groups become so genetically different they can no longer produce offspring together. 5. A new species is officially formed.
Allopatric and Sympatric Speciation
Allopatric Speciation: Speciation that occurs when a population is physically separated by a geographic barrier (e.g., mountains, rivers). * The separation prevents interbreeding, and the groups evolve into different species over time. * Vicariance: When a population is split apart by a new physical barrier like a rising mountain range or a changing river course. * Dispersal: When organisms move to a new area away from the original population. * Examples: Frogs separated by geographic barriers, California and Black-tailed Gnatcatchers, Terns in different regions, Salamander populations separated by barriers, and Finches (via vicariance).
Sympatric Speciation: Speciation that occurs without geographic separation; populations become different species while living in the same environment. * Ecological Niche: Animals (like fish in a lake) may start using different food sources or habitats within the same area until they no longer interbreed. * Polyploidy: Commonly seen in plants, this occurs when an organism acquires extra sets of chromosomes, making them unable to reproduce with the original population and creating a new species immediately.
Adaptive Radiation and Historical Biogeography
Adaptive Radiation: When one species rapidly evolves into many different species. This typically occurs after mass extinctions, on isolated islands, or when organisms enter new environments with available niches and resources.
Panamanian Isthmus: The formation of the Panamanian isthmus connected North and South America. * Terrestrial Impact: It allowed land animals to migrate between continents and inhabit new environments. * Aquatic Impact: It separated ocean populations, stopping gene flow between marine species and leading to allopatric speciation.
Structural Evolution and Phylogeny
Exaptation: A trait that originally evolved for one function but was later co-opted for a different function (e.g., feathers may have first evolved for warmth before being used for flight).
Evolutionary Novelties: These are completely new structures or traits that evolve over time, differing from exaptations which are existing traits used for new purposes.
Is Evolution Goal-Oriented? No. Evolution happens because organisms adapt to their current environment; it is not driven by a "want" or "need" for a specific future trait.
Taxonomic Order (Highest to Lowest): 1. Domain 2. Kingdom 3. Phylum 4. Class 5. Order 6. Family 7. Genus 8. Species
Closeness of Groups: Species within the same genus are more closely related than species that only share the same family or order.
Phylogeny: A diagram showing the evolutionary history and relationships between organisms, including common ancestors and shared traits.
Ancestral vs. Derived Traits: * Ancestral Trait: A characteristic that existed in the common ancestor. * Derived Trait: A modified or new version of a trait that evolved later.
Synapomorphy: A shared, derived trait found in a group of organisms. On a phylogeny, these are displayed on the branches where the trait first evolved.
Key Terms Glossary
Genetic diversity: Variation among individuals of the same species.
Adaptive potential: Ability of a population to adapt to changes due to diversity.
Population: Interbreeding group of the same species in the same area.
Microevolution: Small-scale change in allele frequencies.
Macroevolution: Large-scale change leading to new species.
Deleterious mutation: A harmful mutation decreasing fitness.
Gene flow: Allele movement through migration.
Genetic drift: Random allele changes, common in small populations.
Founder effect: Allele frequency change from a small founding group.
Genetic bottleneck: Reduction in population causing loss of diversity.
Natural selection: Nonrandom survival of the fittest traits.
Biological fitness: Measure of reproductive success.
Adaptation: Heritable survival trait.
Selective pressure: Environmental factor making survival difficult.
Sexual selection: Selection based on attractiveness for mating.
Sexual dimorphism: Physical differences between sexes.
Coevolution: Reciprocal evolutionary influence between species.
Biological species concept: Interbreeding group reproductively isolated from others.
Reproductive isolation: Inability to interbreed or exchange genes.
Allopatric speciation: New species formed by geographic barriers.
Adaptive radiation: Rapid evolution from one species into many.
Sympatric speciation: New species formed without geographic barriers.
Ecological niche: A species' specific role and resource use in an ecosystem.
Polyploidy: Having more than two sets of chromosomes.
Exaptation: A trait co-opted for a new use.