Biology Concepts FINAL Notes PDF

Notes for Chapter 1 The properties of life include order, reproduction, growth and development, energy processing, regulation, response to the environment, and evolutionary adaptation. The diversity of life is arranged into three domains (taxonomy) and includes unicellular organisms: Bacteria, Arch...

Notes for Chapter 1 The properties of life include order, reproduction, growth and development, energy processing, regulation, response to the environment, and evolutionary adaptation. The diversity of life is arranged into three domains (taxonomy) and includes unicellular organisms: Bacteria, Archaea, and Eukarya. Bacteria and Archaea (more extreme and living in more cold areas) are prokaryotes that contain organisms with simple cells. They are singled celled organisms lacking a nucleus, but they diBer in their DNA and cellular structures. Eukarya (living things) includes various protists and the kingdoms Fungi, Plantae, and Animalia. Encompasses all organisms with a nucleus that include plants, animals, fungi, and protists. *A human is classified in domain Eukarya and kingdom Animalia because humans are animals, and animals are eukaryotes. The Process of Science Science uses an evidence-based process of inquiry to investigate the natural world. The scientific approach involves observations, hypotheses, predictions, tests of hypotheses via experiments or additional observations, and analysis of data. A scientific theory is broad in scope and supported by a large body of evidence.  Theory- a well-supported explanation of natural phenomenon that’s based on evidence and repeated testing. In an experimental test of a hypothesis, researchers often manipulate one component in a system and observe the eBects of this change. Independent variable- the factor that is manipulated. Dependent variable- the measurement used to judge the outcome of the experiment (depends on the manipulated variable) Controlled experiment- compares an experimental group with a control group. Control group- an experiment yields data against which another group are compared. Forming a testing hypothesis are at the core of science. This endeavor is influenced by three spheres: 1. Exploration and discovery, 2. Analysis and feedback from the scientific community, and 3. Societal benefits and outcomes. Types of experiments: Natural and manipulative Natural- a study where the experimental and control conditions are determined by nature or other factors outside of the researcher’s control. Manipulative experiments- where the researchers intentionally change a variable to see how it aBects other variables. Five Unifying Themes in Biology Life is distinguished by its unity and its diversity. The scientific explanation for this unity and diversity is evolution, the process of change that has transformed life on Earth from its earliest forms to the vast array of organisms living today. Darwin synthesized the theory of evolution by natural selection. Natural selection- a mechanism that explains how organisms evolve and adapt to their environment over time.  DNA is responsible for heredity and for programming the activities of a cell by providing the blueprint for proteins. A gene is a segment of DNA that directs the synthesis of a specific protein. The flow of information is from DNA transcribed to RNA, which then translates into a chain of molecules that make up protein. Energy flows through an ecosystem in one direction: Entering as sunlight, Converted to chemical energy by producers, Passed on to consumers, and Exiting as heat. Ecosystems are characterized by the cycling of matter: From the atmosphere and soil, Through producers, consumers, and decomposers, Then back to the environment. The study of life extends from the microscopic scale of the molecules and cells that make up an organism to the global scale of the living planet. Emergent properties are the result of interactions between the components of a system. Using an approach called systems biology, scientists attempt to model the behavior of biological systems by analyzing the interactions among their parts. Notes For Chapter 2 Living organisms are composed of matter. Matter is composed of chemical elements.  About 25 elements are essential for human life. Four elements make up about 96% of the weight of most living organisms. ~4% are “trace elements. Some trace elements are required to prevent disease. Fluoride is usually added to municipal water and dental products to help reduce tooth decay. Several chemicals are added to food to Help preserve it Make it more nutritious Make it look better Each element consists of one kind of atom. An atom is the smallest unit of matter that still retains the properties of an element. Three subatomic particles are relevant to our discussion of elements. Neutrons and protons are packed into an atom’s nucleus. Electrons orbit the nucleus. The unique number of protons is an element’s atomic number. An atom’s mass number is the sum of its protons and neutrons in the nucleus. The atomic mass is approximately equal to its mass number. Isotopes of an element have the same number of protons but diBerent numbers of neutrons. The innermost electron shell of an atom can hold up to two electrons. This is the maximum number of electrons that can occupy the innermost electron shell. Radioactive isotopes are useful as tracers for monitoring the fate of atoms in living organisms. Sophisticated imaging instruments can detect them. Chemical Bonds Electrons can be in located in diBerent electron shells, each with a characteristic distance from the nucleus. An atom whose outer electron shell is not full tends to interact with other atoms and share, gain, or lose electrons, resulting in attractions called chemical bonds. The actual transfer of an electron between atoms results in an attraction called an ionic bond. In a covalent bond, atoms do not transfer electrons but share electrons between them. In a nonpolar covalent bond, electrons are shared equally. In polar covalent bonds, such as those found in water, electrons are pulled closer to the more electronegative atom. An ion is an atom or muscle with an electrical charge resulting from gain or loss of one or more electrons. Two ions with opposite charges attract each other. When the attraction holds the ions together, it is called an ionic bond. Salt is a synonym for an ionic compound. One of the most important types of weak bonds is the hydrogen bond. The hydrogen atoms of a water molecule are attached to oxygen by polar covalent bonds. Because of these polar bonds and the wide V shape of the molecule, water is a polar molecule. Water has an unequal distribution of charges.  Water’s Life- Supporting properties The tendency of molecules of the same kind to stick together is cohesion The clinging of one substance to another is adhesion. Cohesion is related to surface tension-a measure of how diBicult is to break the surface of a liquid. Thermal energy is the energy associated with the random movement of atoms and molecules. Thermal energy in transfer from a warmer to a cooler body matter is defined as heat Temperature measures the intensity of heat. When a substance evaporates, the surface of the liquid that remains behind cools down; this is the process of evaporative cooling. Water can exist as a gas, liquid, or solid. Water is less dense as a solid than a liquid because of hydrogen bonding. When water freezes, each molecule forms a stable hydrogen bond with its neighbors. As ice crystals form, the molecules are less densely packed than in liquid water. Because ice is less dense than water, it floats. A solution is a liquid consisting of a uniform mixture of two or more substances. Water’s versatility as a solvent, a dissolving agent, results from the polarity of its molecules. Polar or charged solutes dissolve when water molecules surround them, forming aqueous solutions. The study of life extends from the microscopic scale of the molecules and cells that make up an organism to the global scale of the living planet. Emergent properties are the result of interactions between the components of a system. Using an approach called systems biology, scientists attempt to model the behavior of biological systems by analyzing the interactions among their parts. In liquid water, a very small percentage of water molecules break apart into ions. We use the pH scale to describe how acidic or basic a solution is. A buBer minimizes changes in pH Carbon dioxide is The main product of fossil fuel combustion Increasing in the atmosphere Linked to global climate change About 25% of this human generated CO2 is absorbed by the vast oceans CO2 dissolved in seawater lowers the pH of the ocean in a process known as ocean acidification. In a controlled experiment, scientists looked at the eBect of decreasing carbonate ion concentration on the rate of calcium deposition by reef organisms. The lower the concentration of carbonate ions, the lower the rate of calcification, and thus the slower the growth of coral animals Notes For Chapter 3 Introduction to Organic Compounds Carbon’s ability to bond with four other atoms is the basis for building large and diverse organic compounds. Carbon’s chains form the backbone of most organic molecules. Isomers have the same molecular formula but diBerent structures. Example: Hydrocarbons (C+H only) Hydrocarbons are composed of only carbon and hydrogen. Hydrophilic functional groups give organic molecules specific chemical properties. Functional Groups: Key chemical groups determine molecular properties (e.g., hydroxyl, carbonyl, carboxyl, amino, phosphate). Building Life’s Molecules Macromolecules They can also be called polymers because they are made from identical or similar building blocks strung together. The building blocks of polymers are called monomers. Monomers are linked together to form polymers through dehydration reactions Polymers Polymers are broken apart by hydrolysis. Consists of starch, DNA, chitlin, and cellulose These reactions are mediated by enzymes, specialized macromolecules that speed up reactions. The four classes of biology molecules (macromolecules) contain very large molecules: 1. Carbohydrates Carbohydrates range from small sugar molecules (monomers) to large polysaccharides. Sugar monomers are monosaccharides. Generally has a formula that is a multiple of CH2O and contains hydroxyl groups and a carbonyl group. Cellulose is structural, found in plant cell walls 2. Lipids Are diverse hydrophobic (water-“fearing”) compounds composed largely of carbon and hydrogen. Fats: Energy storage; saturated (animal fats) vs. unsaturated (plants oils). Phospholipids: Key in cell membranes Steroids include cholesterol and some hormones. Proteins: Diverse functions: enzymes, transport, defense, hormones, structure. Made of amino acids linked by peptide bonds Protein structure level: Primary (sequence), Secondary (folds/coils), Tertiary (3D shape), Quaternary (multiple chains) Nucleic Acids: DNA: Double helix; stores genetic info RNA: Single strand; helps build proteins Made of nucleotides (sugar, phosphate, nitrogen base) Dehydration Reaction: Joins monomers into polymers by removing water Hydrolysis: Breaks down polymers into monomers by adding water Notes For Chapter 4 Introduction to the Cell 1. Microscopy: o Light Microscopes: Show living cells. o Electron Microscopes (SEM & TEM): Reveal cell ultrastructure (higher resolution). o Cell Theory: All living things are made of cells; all cells come from pre-existing cells. 2. Cell Size and Surface Area: o Small cells have a high surface area-to-volume ratio, crucial for efficient exchange of materials. o Plasma Membrane: A phospholipid bilayer with embedded proteins; regulates transport. Types of Cells 1. Prokaryotic Cells:  oDomains: Bacteria and Archaea. oFeatures: No nucleus, no membrane-bound organelles, smaller and simpler. 2. Eukaryotic Cells: o Domain: Eukarya (includes protists, fungi, plants, animals). o Features: Nucleus, membrane-bound organelles, compartmentalized functions. Eukaryotic Cell Structure Eukaryotic cells are grouped into four functional categories: 1. Genetic Control Nucleus: o Contains DNA; directs protein synthesis via mRNA. o Nucleolus: Site of ribosome assembly. Ribosomes: Are composed of ribosomal RNA. Synthesize proteins. 2. Manufacturing, Distribution, and Breakdown Endomembrane System: Interconnected organelles for synthesis and transport. o Smooth ER: Makes lipids; processes toxins. o Rough ER: Produces membranes and proteins. o Golgi Apparatus: Modifies, sorts, ships cell products. o Lysosomes: Digestive enzymes for recycling and breakdown. o Vacuoles: § Plants: Central vacuole stores water, nutrients, waste. § Protists: Contractile vacuoles expel water. 3. Energy Processing Mitochondria: Site of cellular respiration; converts food energy into ATP. Chloroplasts (plants & algae): Site of photosynthesis; convert solar energy into sugar. 4. Structural Support, Movement, and Communication Cytoskeleton: o Composed of microtubules, intermediate filaments, and microfilaments. o Functions: Shape, organelle movement, and cell motility. Cell Surface Structures: o Cilia & Flagella: Move the cell or substances. o Extracellular Matrix (ECM): Supports animal cells and communicates with the cytoskeleton. o Cell Junctions: § Tight Junctions: Seal cells together.  § Anchoring Junctions: Provide strength. § Gap Junctions: Allow communication. Plant Cells vs. Animal Cells Plant Cells: o Have a cell wall (made of cellulose) for support. o Contain chloroplasts and a central vacuole. Animal Cells: o Lack cell walls. o Have ECM and more diverse junctions. Energy Evolution Endosymbiont Theory: Mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotes. Notes for Chapter 5 Notes for Chapter 6 Introduction to Cellular Respiration Cellular respiration is essential for breaking down sugars and generating ATP, the primary energy source for cells, which occurs in the presence of oxygen. Brown fat cells have a unique respiration process that produces heat without creating ATP. Energy Dynamics in Ecosystems All life depends on energy, ultimately sourced from sunlight in ecosystems. Photosynthesis rearranges carbon dioxide and water into organic molecules while releasing oxygen. The Relationship Between Breathing and Cellular Respiration Respiration involves gas exchange, where organisms inhale oxygen and exhale carbon dioxide. Breathing supplies the oxygen necessary for cellular respiration and facilitates the removal of waste byproducts. Cellular Respiration and ATP Production Cellular respiration is an exergonic process that converts glucose into ATP, capturing about 34% of energy stored in glucose and releasing the rest as heat. The human body relies on ATP for maintenance and voluntary activities, necessitating a continuous supply of energy. Mechanisms of Energy Capture Cells capture energy from the oxidation of fuel molecules, with electrons transferred to NAD+, creating NADH, which transports electrons to the electron transport chain. The process of oxidative phosphorylation, involving electron transport and chemiosmosis, generates the majority of ATP during cellular respiration. Stages of Cellular Respiration Glycolysis: Occurs in the cytosol and breaks glucose down into pyruvate, yielding 2 ATP and 2 NADH []. Pyruvate Oxidation and Citric Acid Cycle: Takes place in mitochondria, completing glucose breakdown into carbon dioxide and water []. Oxidative Phosphorylation: Involves electron transport chains, where most ATP is produced, as electrons are passed to oxygen, forming water []. Detailed Process of Glycolysis Glycolysis involves an energy investment phase that consumes ATP to transform glucose into two three-carbon intermediates. The overall outcome of glycolysis is the breakdown of one glucose molecule into two pyruvate molecules, yielding a net gain of 2 ATP. Glycolysis comprises nine chemical reactions, with products from one reaction serving as reactants for the next, showcasing metabolic pathways. Summary of Cellular Respiration's Importance Cellular respiration is crucial for energy banking in ATP molecules, driving all cellular activities and maintaining a balance of energy intake and expenditure. Essential queries regarding the chemical characteristics of oxygen and its role in respiration are posed to provoke deeper understanding Citric Acid Cycle The oxidation of pyruvate results in the formation of acetyl CoA, CO2, and NADH. Each turn of the Citric Acid Cycle involves: Addition of two carbons from acetyl CoA. Release of two CO2 molecules. Production of three NADH and one FADH2. ATP Production Most ATP is produced via oxidative phosphorylation in mitochondria. Electrons from NADH and FADH2 are transferred through the electron transport chain to O2, forming water. The energy from redox reactions is utilized to pump H+ ions into the intermembrane space, creating a gradient. Chemiosmosis drives H+ back through ATP synthase, facilitating ATP synthesis. Fermentation Under anaerobic conditions, cells like muscle cells, yeast, and certain bacteria can produce ATP through glycolysis. NADH is converted back to NAD+ as pyruvate is reduced to: Lactate (lactic acid fermentation). Alcohol and CO2 (alcohol fermentation). Two types of fermentation are mentioned, each allowing for the regeneration of NAD+. Evolutionary Context Glycolysis is a universal process occurring in the cytosol of nearly all organisms, believed to have evolved in ancient prokaryotes. Characteristics of glycolysis suggest its ancient nature as a metabolic pathway. Utilization of Organic Molecules Cells can derive energy from various organic molecules including: Carbohydrates (e.g., sucrose, starch). Fats. Proteins. A checkpoint question discusses the feasibility of surviving on a diet high in fats and proteins with minimal sugar. Biosynthesis and Metabolic Regulation Intermediates from cellular respiration and ATP are used for the biosynthesis of other organic molecules. Metabolic pathways are often regulated through feedback inhibition. A checkpoint question addresses weight gain and fat storage on a low-fat diet, emphasizing the complexity of metabolism. Notes For Chapter 7 Notes For Chapter 8 Cell Division and Its Roles Cell division is essential for the reproduction of cells and organisms, originating from preexisting cells. Asexual reproduction leads to offspring that are genetic clones of the parent, while sexual reproduction results in genetically diverse offspring. Prokaryotic Reproduction Prokaryotic cells reproduce asexually through binary fission, where the cell divides in half. Most prokaryotes have a single circular DNA molecule that serves as their chromosome. The binary fission process involves chromosome replication, separation, and membrane pinching to create two daughter cells. Eukaryotic Cell Cycle and Mitosis Eukaryotic cells possess multiple chromosomes within the nucleus, containing more genes than prokaryotes. Chromosomes duplicate before cell division, forming sister chromatids that are identical and joined together. The cell cycle consists of ordered events from cell formation to division, including growth and preparation phases. Mitosis Process Mitosis involves the distribution of duplicated chromosomes into two daughter nuclei through a series of dynamic changes. Sister chromatids separate and move to opposite poles of the cell, followed by the formation of two new nuclei. Cytokinesis Cytokinesis is the final step in cell division, occurring differently in plant and animal cells. In animal cells, a cleavage furrow forms as the cell constricts, while in plant cells, a cell plate develops to divide the cell. Regulation of Cell Division Environmental factors influence the rate of cell division, with normal cells requiring surface attachment and growth factors to divide. A set of proteins controls the cell cycle, with specific checkpoints determining whether a cell proceeds to division. Cancer and Cell Division Cancer cells exhibit uncontrolled division, forming malignant tumors that can invade other tissues. Treatments like radiation and chemotherapy target cell division to combat cancer. Individual factors such as age and race affect cancer treatment outcomes, advocating for personalized approaches in research and treatment strategies Chromosomes and Chromosomal Pairs Somatic cells in species, including humans, contain a specific number of chromosomes (e.g., humans have 46). Chromosomes are arranged in homologous pairs, with each pair carrying genes for the same characteristics at identical loci. Gametes and Chromosome Sets Diploid cells contain two sets of homologous chromosomes, while gametes (eggs and sperm) are haploid, having a single set of chromosomes. Sexual life cycles alternate between haploid and diploid stages. Meiosis Process Meiosis involves two rounds of cell division following chromosome duplication, resulting in four daughter cells. The first division (meiosis I) pairs homologous chromosomes and involves crossing over, where segments are exchanged between nonsister chromatids. Meiosis II resembles mitosis, separating sister chromatids to produce four haploid cells. Genetic Variation Mitosis produces two identical diploid daughter cells, while meiosis produces four genetically unique haploid gametes. Independent orientation of chromosomes during metaphase I and random fertilization contribute to genetic diversity among offspring. Crossing over during prophase I enhances genetic recombination and variability in gametes. Chromosomal Abnormalities Nondisjunction can lead to an abnormal chromosome count, resulting from failure of homologous chromosomes or sister chromatids to separate properly during meiosis. A karyotype provides a photographic inventory of chromosomes, helping to detect chromosomal abnormalities. Specific Conditions Trisomy 21 (Down syndrome) is caused by an extra copy of chromosome 21. Abnormal numbers of sex chromosomes can lead to conditions like Klinefelter syndrome and Turner syndrome, with varying effects on health and fertility. Notes For Chapter 9 Introduction to Genetics Over 12 million Americans have explored their genetic makeup as of 2018, reflecting a growing interest in genetics. Genetic testing services provide extensive reports on individual genetic information. Historical Context Hippocrates's Pangenesis: The incorrect theory that body parts contribute to reproductive cells was highlighted. Blending Hypothesis: This hypothesis was rejected for failing to explain the re-emergence of traits in later generations. Mendel's Contributions Genetics, the scientific study of heredity, was pioneered by Gregor Mendel through experiments with pea plants. Key terms include: Character: A heritable feature that varies among individuals. Alleles: Alternative versions of genes that account for variations in traits. Mendel’s Laws Law of Segregation: Each organism inherits two alleles for each gene, one from each parent. Alleles separate during gamete formation, leading to a 3:1 phenotypic ratio in offspring. Homozygous vs. Heterozygous: Homozygous: Two identical alleles. Heterozygous: Two different alleles. Chromosomal Basis of Inheritance Diploid cells contain homologous chromosome pairs, with each chromosome carrying alleles for the same genes. The law of segregation is grounded in the process of meiosis. Independent Assortment Monohybrid Cross: A cross between individuals heterozygous for one character. Dihybrid Cross: A cross between individuals heterozygous for two characters. Mendel's law of independent assortment states that allele pairs segregate independently during gamete formation. Testcrosses and Unknown Genotypes A testcross involves mating an individual of unknown genotype with a homozygous recessive individual to reveal the unknown genotype. Probability in Genetics Rule of Multiplication: Calculates the probability of two independent events occurring together. Rule of Addition: Calculates the probability of an event occurring in different ways. Application to Human Genetics Many human traits follow Mendelian inheritance patterns, and family pedigrees are useful for tracking these traits. Genetic disorders can be inherited as either dominant or recessive traits, often affecting offspring of normal carrier parents. Conclusion - The document highlights the relevance of Mendel’s principles in modern genetics, emphasizing their application in understanding human traits and genetic disorders. Variations on Mendel’s Laws Mendel’s laws apply to all sexually reproducing species, but the relationship between genotype and phenotype can be complex. Complete dominance is when offspring resemble one of the parental varieties, while incomplete dominance results in intermediate phenotypes. Incomplete Dominance Incomplete dominance occurs when F1 hybrids show traits that are a blend of the parental phenotypes. Codominance The ABO blood group system in humans illustrates codominance, with IA and IB alleles being expressed in heterozygous individuals (type AB blood). Understanding parental genotypes is essential in predicting offspring phenotypes in blood types. Pleiotropy One gene can influence multiple phenotypic traits, exemplified by sickle-cell disease, which affects hemoglobin, red blood cell shape, anemia, and organ health. Sickle-cell and nonsickle alleles are codominant, and carriers exhibit increased resistance to malaria. Polygenic Inheritance Many traits are influenced by multiple genes, a phenomenon known as polygenic inheritance, with human height serving as a prime example. Environmental Influences Traits are often shaped by a combination of genetic and environmental factors, although Mendel's pea plant studies allowed him to overlook environmental influences due to controlled conditions. Chromosomal Basis of Inheritance The chromosome theory of inheritance states that genes are located on chromosomes and that these chromosomes undergo segregation and independent assortment during meiosis. Mendel’s laws are physically represented in the behavior of chromosomes during meiosis. Linked Genes Genes located close together on the same chromosome are termed linked genes and tend to be inherited together, as shown in studies by Bateson and Punnett. Crossing Over Crossing over during meiosis generates new allele combinations, leading to recombinant gametes, which can affect inheritance patterns. Sex Chromosomes In mammals, males have XY chromosomes and females have XX, with the Y chromosome determining male characteristics. Certain species have alternative sex determination mechanisms based on environmental factors, such as temperature in reptiles. Sex-Linked Genes Genes located on sex chromosomes exhibit unique inheritance patterns, as seen in the inheritance of traits like eye color in fruit flies. X-linked disorders are more prevalent in males due to their having only one X chromosome. Human Sex-Linked Disorders Most X-linked disorders, being recessive, primarily affect males, requiring females to inherit the allele from both parents to manifest the disorder. Notes For Chapter 10 Structure of Genetic Material DNA and RNA are types of nucleic acids made up of long chains of nucleotides. Each nucleotide consists of a nitrogenous base, a five-carbon sugar, and a phosphate group. The nucleotides are linked together by a sugar-phosphate backbone. Differences Between DNA and RNA DNA stands for deoxyribonucleic acid and contains deoxyribose sugar and the bases adenine (A), cytosine (C), thymine (T), and guanine (G). RNA stands for ribonucleic acid, contains ribose sugar, and uses uracil (U) instead of thymine. DNA Structure DNA is described as a double-stranded helix. Each strand of DNA contains a specific sequence of nucleotides, which can be complementary to the other strand. DNA Replication Process DNA replication begins with the separation of the two DNA strands. Each strand serves as a template for creating a complementary strand from free nucleotides. The process follows a semiconservative model, resulting in new DNA helices that consist of one old strand and one new strand. Mechanisms of DNA Synthesis The enzyme DNA polymerase synthesizes one daughter strand continuously while the other strand is created in short segments. Short pieces of the lagging strand are connected by the enzyme DNA ligase, ensuring the integrity of the DNA molecule during replication. The DNA of a gene is transcribed into RNA, which is translated into a polypeptide. Transcription is the synthesis of RNA under the direction of DNA. Translation is the synthesis of protein under the direction of RNA. Notes For Chapter 13 Introduction Evolution explains the diversity of life and is ongoing. The environment plays a key role in shaping evolutionary changes. Key Concepts 13.1 Darwin’s Theory of Evolution Darwin’s On the Origin of Species introduced the idea of "descent with modification." Evolution connects all life through common ancestry and adaptations over time. Natural selection is the driving mechanism of evolution. 13.2 Fossil Evidence Fossils show differences between past and present organisms and trace evolutionary sequences. The fossil record documents species’ extinctions and transitions. 13.3 Transitional Fossils Fossils link extinct and living species, such as the discovery of Pakicetus and Rodhocetus, showing whales' evolution from land mammals. 13.4 Homologies as Evidence for Evolution Homology: Similarities in traits due to common ancestry. o Structural and molecular homologies link species. o Vestigial structures are remnants of ancestral features. 13.5 Evolutionary Trees Evolutionary trees depict relationships and branching sequences based on anatomical and molecular homologies. 13.6 Natural Selection Mechanism Darwin observed artificial selection and applied its principles to natural populations. Key points about natural selection: o Populations evolve, not individuals. o Only heritable traits are affected. o Evolution is not goal-directed. 13.7 Observing Natural Selection Examples include pesticide resistance in insects. Natural selection acts as an editing, not creative, process. 13.8 Sources of Genetic Variation Mutation is the ultimate source of genetic variation. Sexual reproduction generates diversity through: o Crossing over during meiosis. o Independent chromosome orientation. o Random fertilization. 13.9 Evolution in Populations A population is a group of interbreeding individuals of the same species. Evolution occurs through changes in the gene pool (microevolution). Individuals do not evolve—populations do. Notes For Chapter 13.10 The Hardy-Weinberg Equilibrium Populations not evolving meet five conditions: 1. Large population size. 2. Random mating. 3. No mutations. 4. No gene flow. 5. No natural selection. The Hardy-Weinberg equation evaluates whether a population is in equilibrium or evolving. 13.12 Mechanisms of Microevolution  Natural Selection: Consistently leads to adaptive evolution by favoring traits that increase survival or reproduction. Genetic Drift: Random events (e.g., bottleneck or founder effects) reduce genetic diversity. Gene Flow: Movement of alleles between populations, which can interfere with local adaptations. 13.13 Natural Selection Only natural selection produces traits that increase an organism’s relative fitness. Adaptive traits become more prevalent over generations. 13.14 Natural Selection and Phenotypic Variation Natural selection alters phenotypic variation in three patterns: 1. Stabilizing Selection: Favors intermediate traits. 2. Directional Selection: Favors one extreme. 3. Disruptive Selection: Favors both extremes over intermediates. 13.15 Sexual Selection A form of natural selection focused on reproductive success. Intrasexual Selection: Competition within the same sex for mates. Intersexual Selection (Mate Choice): Individuals of one sex (usually females) select mates based on traits. Sexual dimorphism arises from such selection. Limits of Natural Selection Evolution cannot produce perfection due to: o Constraints of existing variations and historical structures. o Adaptations being compromises. o Environmental unpredictability and chance events. Notes For Chapter 14 14.1 The Origin of Species and Biological Diversity Microevolution: Small changes in a population’s gene pool across generations. Speciation: The process where one species splits into two or more, driving both the unity and diversity of life. 14.2 Defining a Species  Biological Species Concept: A species is a group of populations capable of interbreeding and producing fertile offspring but reproductively isolated from other groups. Other definitions include: o Morphological Species Concept: Based on physical traits; applicable to asexual organisms and fossils. o Ecological Species Concept: Defined by ecological niches and roles in the environment. o Phylogenetic Species Concept: The smallest group sharing a common ancestor, forming a branch on the tree of life. 14.3 Reproductive Barriers Prevent interbreeding and maintain species isolation. Categories: o Prezygotic Barriers: Prevent mating or fertilization (e.g., temporal isolation, habitat isolation). o Postzygotic Barriers: Affect hybrid viability or fertility (e.g., hybrid sterility, reduced hybrid viability). 14.4 Allopatric Speciation Geographic separation can lead to the formation of new species by isolating populations. Evolutionary mechanisms: o Natural Selection: Adapts populations to their environments. o Mutation: Introduces genetic variation. o Genetic Drift: Alters gene pools in small populations. Study Questions 1. Microevolution vs. Speciation: How do these processes differ in their effects on populations? 2. Species Concepts: Compare the biological, morphological, ecological, and phylogenetic definitions of a species. 3. Reproductive Barriers: What are the key differences between prezygotic and postzygotic barriers? 4. Allopatric Speciation: How does geographic isolation drive the development of new species? This guide explores the mechanisms of speciation, reproductive isolation, and how diversity arises in biological communities. 14.5 Evolution of Reproductive Barriers  Reproductive barriers develop as populations adapt to different environmental conditions (e.g., food sources, pollinators, predators). Example: Female Galápagos finches prefer songs of males from their own island, reinforcing species divergence. 14.6 Sympatric Speciation Occurs without geographic isolation, often through: o Polyploidy: Chromosome duplication, common in plants. o Habitat Differentiation: Use of distinct resources within the same environment. o Sexual Selection: Mate preferences driving speciation. 14.7 Sexual Selection and Speciation Sexual selection has driven speciation in certain species, such as cichlids in Lake Victoria. Studies of such species highlight the role of mate choice in diversification. 14.8 Adaptive Radiation on Islands Isolated islands foster speciation through: o Repeated isolation and recolonization. o Evolution of unique species from a common ancestor. Example: Galápagos finches showcase adaptive radiation due to varied ecological niches. 14.10 Hybrid Zones Regions where closely related species meet and mate, producing hybrid offspring. Outcomes: o Reinforcement: Strengthening reproductive barriers. o Fusion: Reversal of speciation via increased gene flow. o Stability: Continued production of hybrid offspring.