Chapters 18-21 Biology II Exam Study Guide
Chapters 18-21 Biology II Exam Study Guide Biol 2061
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Chapter 18: The Origin and History of Life The four stages of life: 1. Nucleotides and amino acids were produced prior to the existence of cells 2. Nucleotides became polymerized to form RNA and DNA and amino acids polymerize to make proteins 3. Polymers are then enclosed in membranes 4. Polymers enclosed in membranes acquired cellular properties. ● Reducing atmosphere hypothesis: the hypothesis that states that the early earth atmosphere was rich in water vapor, hydrogen, methane, and ammonia, and oxygen, which produced a reducing atmosphere because methane and ammonia readily give up electrons to other molecules. Such oxidation-reduction (redox) reactions are required for the formation of complex organic molecules. ● Extraterrestrial hypothesis: the hypothesis that organic molecules may have been present in meteorites, which may contain a substantial amount of organic carbon including amino acids and nucleic acid bases. ● Deep sea vent hypothesis: the hypothesis which states that organic molecules may have originated in deep sea vents, where superheated water rich in metal ions and hydrogen sulfide mixes abruptly with cold water. ● How clay allows for polymers to form: the purine bases of RNA interact with the silicate surfaces of the clay, cations (+) such as Mg++ bind the nucleotides to the negative surfaces of the clay, binding the phosphate of one nucleotide to the ribose of the next. Key features of protobionts: 1. Have boundaries (membranes) which separate internal contents from external environments. 2. Polymers inside boundary contain information 3. Polymers inside boundary have catalytic functions 4. The protobionts eventually developed the capability of self-replication. Protobionts didn't replicate precisely like other organisms, but just divided to replicate. ● The critical step allowing for protobionts to self replicate: the dividing protobionts exhibited metabolic pathways which would change the organic molecule structures. The polymers inside protobionts must have gained the catalytic ability to link organic building blocks together for new polymers. ● Metabolic pathways became more complex and the ability of self replication become more refined over time. ● Coacervates: droplets that form spontaneously from the association of charged polymers such as proteins, carbohydrates, or nucleic acids surrounded by water. ● Surrounded by a tight skin of water ● Possess osmotic properties ● The boundary allows the selective absorption of simple molecules from the surrounding medium ● Enzymes trapped within the coacervate can perform simple metabolic functions. Protobionts may have resembled liposomes Liposome: a vesicle surrounded by a lipid bilayer. ● selectively permeable ● Store energy in form of an electrical gradient ● Liposomes which discharge energy in a neuron-like fashion shows rudimentary signs of excitability, a characteristic of living cells. The majority of scientists favor that RNA was the first macromolecule that was found in protobionts. RNA has three key functions: 1. RNA has the ability to store information in its nucleotide sequence 2. Due to base pairing, its nucleotide sequence has the ability of self replication. 3. Ribozymes: RNA molecules which catalyze chemical reactions. DNA has a very limited catalytic function, and proteins are not known to undergo self-replication. RNA can perform functions that are of the characteristics of proteins and have the self-replication properties of DNA, serving as genetic material with replicative functions. ● Researchers believe that RNA molecules that were first made prebiotically evolved into more complex molecules which produced cell-like characteristics by a process called chemical selection. ● Chemical Selection: when a chemical within a mixture has special properties or advantages that cause it to increase in number relative to other chemicals in the mixture. ● Chemical selection leads to chemical evolution, in which the population of molecules changes over time to become a new population with a different chemical composition. The RNA World is a hypothetical period of time on Earth when living cells had both the information needed for life and the catalytic activity in RNA molecules alone. ● Chemical selection can change the functional characteristics of a group of RNA molecules over time by increasing the proportion of those molecules with enhanced function. Why RNA was superseded by DNA & Protein? ● During the RNA world; RNA had 1) store information and 2) catalyze chemical reactions. ● The incorporation of DNA into cells would relieve RNA of its role of storing energy, allowing catalytic functions to increase production and variety. ● Cells with both DNA and RNA would have advantages of those with just RNA and would've been selected. ● DNA also has stability, it is less likely to break spontaneously compared to RNA. ● How DNA came into existence? Reverse transcription: when DNA is made using RNA as a template. How proteins emerged through RNA ● RNA can catalyze the formation of peptide bonds and even attach amino acids to primitive tRNA molecules. 1. mRNA provides the information for a polypeptide sequence. 2. tRNA molecules act as adaptors for the formation of a polypeptide chain. 3. Ribosomes containing rRNA provide a site for polypeptide synthesis. 4. rRNA within the ribosome acts as a ribozyme to catalyze peptide bond formation. 18.2 The Fossil Record ● Fossils are formed in sedimentary rock that were formed from particles of older rocks which were broken apart by wind or water. The particles are like gravel, sand or mud which cover living or dead organisms at the bottoms of rivers, lakes, or oceans and over time the particles build up and eventually are compressed into rock. ● Most fossils are formed when organisms are buried and minerals replace hard parts of the organism over millions of years, making a recognizable representation of the organism. ● The age of fossils are revealed by their location in sediment. The higher up the fossil, the younger it is, the lower in sediment=older. Factors which affect the fossilization of organisms are: ● Whether or not the organism is made of hard or soft tissue ● Anatomy, size, and number of species & environmental factors ● Prokaryotic cells arose during the Archaean eon; all life forms were prokaryotic ● Bacteria and archea share common characteristics suggesting a common ancestor. Heterotrophs: gain energy from the chemical bonds in organic molecules they consume; consume other organisms or materials from other organisms. Autotrophs: gain energy from light or inorganic molecules. Plants are an example of autotrophs converting sunlight into glucose. Heterotrophs rely on autotrophs for the production of food. Which came first? ● Scientists argue that autotrophs could've arisen from the ocean next to deep-sea vents, using chemicals excreted from the vents as a source of energy to make organic molecules. ● A counter: that heterotrophs would have been simpler for the first primitive cells to use the organic molecules in the prebiotic soup as a source of energy. Eukaryotic cells emerged during the proterozoic eon ● In eukaryotic cells, there are 3 organelles which contain DNA ● Mitochondria ● Chloroplasts ● Nucleus Those three organelles each contain their own DNA sequence, suggesting they were once separate, and then came together. ● Endosymbiosis: a relationship in which a smaller organism (the endosymbiont) lives inside a larger organism (the host). This hypothesis works to explain the origin of the nuclear genome. ● An archaeal species evolved the ability to invaginate its plasma membrane, which could have two results 1. Eventually lead to the formation of a nuclear envelope and an internal membrane system. 2. The ability to invaginate the plasma membrane gives the cell a mechanism to take up things via endocytosis. ● The second result could explain how mitochondria and chloroplasts were taken up into eukaryotic cells. Among multicellular organisms there are 3 common characteristics: 1. They arise from a single cell which divides and adheres. 2. The daughter cells could produce a different cell type. 3. As an organism increases in size, the greater percentage which could be somatic cells, which carry out the activities needed for survival. Reproductive cells produce offspring. History of life: ● The phanerozoic eon started 543 MYA to present, this is when the abundance of fossils and life were identified.. ● The Cambrian Period (545-490 MYA),warm & wet. The diversity of animals increased rapidly; this is called the cambrian explosion. ● By the middle of the cambrian period, all of the existing major types of marine invertebrates were present, plus many that became extinct. ● Ex: echinoderms (sea urchins & starfish), arthropods (insects, spiders, crustaceans), mollusks (clams and snails), chordates (organisms with a dorsal nerve chord), and vertebrates (animals with backbones). ● Factors towards the explosion: -increasing oxygen levels -new qualities of species so that they can explore new environments -evolutionary arms race between predator and prey The ordovician period (490-443 MYA). Also warm and wet atmosphere. ● A diverse group of hard-shelled marine invertebrates appeared. ● Early land plants and arthropods appeared on land. The silurian Period (443-417 MYA) relatively stable climate, glaciers melted & oceans rose. ● No new major types of invertebrates, changes among existing vertebrate and plant species. ● Many new types of fishes ● Marked a major colonization of land by terrestrial plants and animals. Species evolved adaptations that prevented them from drying out. ● Ancestral relatives of spiders and centipedes became widespread. ● The earliest vascular plants, which have tissues that are specialized for the transport of water, sugar, and salts throughout the plant body came about. Devonian period 417-354 MYA- ● A major increase in terrestrial plant species. Saw the first trees and forests. ● A major expansion of terrestrial animals, insects appear, other invertebrates increased populations. ● Early tetrapods included amphibians, lived on land but required water to lay eggs ● At the end of this period a prolonged series of extinctions eliminated many marine species. The cause of this mass extinction is unknown. Carboniferous period 354-20 MYA ● Very large plants and trees,first flying insects, giant dragonflies with a wingspan of over 2 feet inhabited forests and swamps. ● Terrestrial vertebrates also became more diverse. ● Amphibians were very widespread ● The amniotic egg was one of the most important evolutionary innovations. Critical for reptiles & tetrapods that laid eggs on land. For reptiles the amniotic egg was covered with a leathery hard shell which prevented the desiccation of the embryo inside. Permian period 290-248 MYA ● Continental drift brought much of the total land together into a supercontinent; pangea. ● The forests of fernlike plants were replaced with gymnosperms, seed- bearing land plants. ● Amphibians prevalent but reptiles became dominant. ● At the end of the Permian period the largest extinction occurred killing 90-95% of marine species and a large proportion of terrestrial species. Chapter 19 intro: Polymorphism: (Multiple-changes) a trait or gene that occurs in many forms; represented by discrete (not continuous) data; not a geographic race or seasonal form. ● Evolution: heritable change in one or more characteristics of a population or species from one generation to the next ● Microevolution: changes in allele frequencies in a population over time. ● Macroevolution: formation of new species groups of species Darwin 3 word definition of evolution: descent with modification Dating of rocks: absolute dates: used by radioactive isotopes; which is an unstable atom in which the nucleus is losing energy to its surroundings. ● A half life is 50% of the period required for the isotope to completely decay The fossil record ● Shows the general trend in the increase of biological diversity: The differences among living organisms (genetic variation). ● Is incomplete for many reasons table 18.1 (see table). Prokaryotes were the 1st & only kinds of life for about 2 billion years. (all life was aquatic until about 500MYA see figure 18.8) ● Biological organisms have changed through time because of ● Genetic changes--chapter 19 ● Environmental variations (see concept 18.3 & HW 1) -can allow for new types of organisms -responsible for many extinctions -meteorite impacts & other major environmental changes can lead to mass extinctions. (theres been at least 5). Boundaries between geologic time periods often are based on these events. ● Endosymbiosis: endo(one partner is enclosed within this second)symbiosis(relationship between two organisms that doesn't always benefit one) Stromatolites: aka Cyanobacteria ● Corals (small animals called cnidarians that contain a unicellular alga). Invagination: ***having genetic material surrounded by a nuclear membrane means that that material is protected by anything that enters the cytosol. (nuclear envelope). **the cell seals off the intruder from the rest of the cell, enclosing it in a membrane. ** cyanobacterium was engulfed by the cell & it gave rise to plastids; aka chloroplasts ---> and photosynthetic organisms. A seconds one didn't engulf the cyanobacterium---> animals Eukaryote is defined as having a nucleus AND organelles. How did endosymbiosis result in a beneficial relationship? ● An anaerobe with an aerobic organism? ● A heterotroph with an autotroph? Why do we think that mitochondria arose before chloroplasts? ● Among modern eukaryotes, who has mitochondria? Who has chloroplasts & other plastids? -mitochondria-- everything -chloroplasts--plants & algae ● Since all have mitochondria then they developed first. 1. Plastids (including chloroplasts) & mitochondria are the only eukaryotic organelles surrounded by 2 membranes. 2. These organelles reproduce via binary fission (a type of cellular division or organelle replication, the genetic material is copied and the cell divides into two parts, each part containing half of the material) These are the only two which do so. 1. Ribosomes of plastids & mitochondria are more similar to those of prokaryotes than to others in eukaryotes 2. mtDNA (mitochondrial DNA) appears to be derived from bacteria, & chloroplast DNA appears to be derived from eukaryotes and cyanobacteria. NEITHER DNA is the same as nuclear DNA. ***mitochondrial DNA only comes from our MOTHERS, it could be used to track maternal lineage. Homework 1: 1. Biologists are interested in the role of clay in the origin of life. They think clay might have catalyzed the formation of organic polymers such as proteins an RNA. 2. Bacteria E. coli are shaped like tiny, straight sausages. They are examples of rods 3. Cyanobacteria belong to the domain of archea 4. The 1st organisms represented prokaryotes. These were anaerobic heterotrophs. 5. Until about 500 million years ago, all living things were aquatic 6. Cyanobacteria form layered structures called stromalites, in both ancient and modern oceans. These photoautotrophs are thought to have added O2 into the atmosphere, thus spelling doom for many anaerobic prokaryotes and allowing evolution of aerobic species. ● Fungi are eukaryotes ● Ferns are eukaryotes ● Humans are eukaryotes ● Photoautotrophs use the sun energy and CO2 carbon source. ● Chemoautotrophs use inorganic chemicals and CO2 carbon source. Prokaryotes are important because: ● They are decomposers which feed upon dead or decaying organisms, thus returning chemical elements to the environment. ● Some prokaryotes cause diseases such as bubonic plague and cholera ● Photosynthetic prokaryotes might have changed early earths atmosphere. ● Interactions with eukaryotes include the manufacture of vitamins in the intestines of humans and other vertebrates. ● We use prokaryotes to remove pollutants from soil, air, and water. Evolution: ● Species ● A group or groups of related organisms that share a distinctive form ● In organisms that reproduce sexually, members of the same species are capable of interbreeding to produce viable & fertile offspring. ● Population: ○ A group consisting of members of the same species that are likely to encounter each other and thus have opportunity to interbreed. ● A theory is a broad statement supported by many testable hypotheses. History of the theory of evolution ● Empirical thought ○ Relies on observation to form an idea or hypothesis, rather than trying to understand life from non-physical or spiritual point of view. ○ Most Europeans thought the earth was young (6,000 years old) that earth didn't change & everything was constant. ● Date of on the origin of species (darwin) was 1859--after this publication people started to see the world in a different way than before in history. ● Darwin coined the phrase "descent with modification" ○ Variation within a given species ○ Heritable characteristics (traits) are passed from parents to offspring ○ Genetic basis was not yet known ● Natural selection ○ More offspring are produced than can survive ○ Individuals compete for limited resources ○ Individuals with superior traits flourish and reproduce. Evidence of evolutionary change: ● Studies of natural selection ○ Pathogens resistant to antibiotics ○ Insects resistant to pesticides ○ The grant's research on galapagos finches ● Biogeography: ○ Study of the geographical distribution of extinct & modern species ○ Isolated continents & island groups have evolved their own distinct plant & animal communities (due to reproductive isolation and differences in agents of natural selection) ■ Endemic- naturally found in only 1 particular location. ○ Ex: island fox evolved from mainland gray fox. ● Convergent evolution: when two species from different lineages show traits (analogs) similar in function because ancestors occupied similar environments, which makes them subjective to similar forces of natural selection. ● Ex: giant anteaters & echidnas both have long snouts and tongues to feed on ants. ● Aerial rootlets for clinging in english ivy and wintercreeper ● Antifreeze proteins in different fish in very cold water. Ch. 19 Evolution and Population Genetics Population Genetics: the study of genes and genotypes in a population. ● Central issue is genetic variation, its extent within populations, why it exists, and how it changes over the course of many generations. ● Empirical thought relies on observation to form an idea or hypothesis rather than trying to understand life from a non-physical or spiritual point of view. ● Endemic- naturally found in only 1 particular location. ● Convergent evolution: two species from different lineages have independently evolved similar characteristics because they occupy similar environments. ● Analogous structures: convergent traits; where characteristics have arisen independently two or more times, because of different species have occupied similar types of environments on the earth. ● Allele: variant forms of a particular gene which determine the trait. ● Homology: a similarity that occurs due to descent from a common ancestor. ● The forelimbs of vertebrates have a similar pattern of bone arrangements, these are homologous structures. They are similar to each other because they have evolved from a common ancestor. ● Vestigial structures: anatomical features that have no current function but resemble structures of their presumed ancestors. ● Molecular homology: a similarity between organisms at the molecular level due to descent from a common ancestor. ● Developmental homology: species that differ as adults often bear striking similarities during embryological development, might or might not persist into adulthood. ● Gene pool: made up of all the alleles for every gene in a given population. Each member of the population receives it genes from its parents, which, contribute to the gene pool of the next generation. ● The term polymorphism refers to the presence of two or more variants or traits for a given character within a population. ● A gene that commonly exists as two or more alleles in a population is a polymorphic gene. ● To be considered a polymorphic gene, the gene must exist in at least two different forms and occur at a frequency that is greater than 1%. ● These may involve several types of changes such as: deletion of a significant region of the gene, a duplication of a region, or a change in a single nucleotide ● Single-nucleotide polymorphism: the smallest type of genetic variation that can occur within a given gene and also the most common. ● Monomorphic gene: exists predominantly as a single allele in a population, when 99% or more of alleles of a given gene are identical in a population, the gene is monomorphic. Two calculations are essential to population genetics: number of copies of a Allele frequency= specific allele in a population over Total number of all alleles for that gene in a population number of individuals with a Genotype frequency= particular genotype in a population Over total number of individuals in a population ● Microevolution: describes changes in a population's gene pool, such as changes in allele frequencies, from generation to generation. What causes microevolution? 1. The introduction of new genetic variation into a population is one essential aspect 2. New alleles of preexisting genes arise by random mutation and new genes can be introduced into a population by gene duplication and horizontal gene transfer. ● Adaptations: changes in populations of living organisms that increase their ability to survive and reproduce in a particular environment. Natural selection & Evolution in molecular genetics 1. Within a population, allelic variation arises from random mutations, causing differences in DNA sequence. A single point mutation may alter the amino acid, thus creating a new allele and may in turn alter the function of the protein. 2. Some alleles encode proteins that enhance an individual's survival or reproductive capability over other members of the population. 3. Individuals with beneficial alleles are more likely to survive and reproduce thus contributing to the gene pool for the next generation. 4. Over many generations, allele frequencies of many different genes change through natural selection, and altering the characteristics of a population. ● Fitness: the relative likelihood that one genotype will contribute tot eh gene pool of the next generation compared with other genotypes. Fitness is a measure of reproductive success. ● Directional selection: individuals at one extreme of a phenotypic range have greater reproductive success in a particular environment. Reasons for this: ○ Populations may be exposed to prolonged change in its living environment & under the new conditions, the relative fitness values may change in favor one genotype, which will promote the elimination of other genotypes. ● Stabilizing selection: favors the survival of individuals with intermediate phenotypes and selects against those with extreme phenotypes. ○ Tends to decrease genetic diversity because it eliminates alleles that cause extreme phenotypes. ● Diversifying selection: (aka disruptive selection) favors the survival of two or more different genotypes that produce different phenotypes. Favors extremes, intermediates are acted against. ○ The fitness values of a particular genotype are higher in one environment and lower in a different one, whereas the fitness values of the second genotype vary in an opposite manner. ○ Likely to occur in populations that occupy heterogeneous environments, so some members of the species are more likely to survive in each type of environmental condition. ● Balancing selection: is a type of natural selection that maintains genetic diversity in a population. How a population can maintain genetic diversity ○ Results in balancing polymorphism: when two or more alleles are kept in balance and therefore are maintained in a population over many generations. ● Two ways balancing selection occurs: 1. Heterozygote advantage: For genetic variation involving a single gene, balancing selection can favor the heterozygote over either corresponding homozygote. ○ This sometimes explains the persistence of alleles that are deleterious in a homozygous condition. 2. Negative frequency-dependent selection: the fitness of a genotype decreases when its frequency becomes higher. Rare individuals have a higher fitness than common individuals. ○ This is thought to maintain polymorphisms among species that are preyed upon by predators. ● Sexual selection: individuals with certain traits are more likely to engage in successful reproduction that others. Powerful form of natural selection. ○ Affects male characteristics more intensely than females. ● Sexual dimorphism: a significant difference between the appearances of the two sexes within a species. ● Intrasexual selection: when members of one sex, usually males, compete with each other for opportunities to mate. ● Intersexual selection: mate choice, members of one sex, usually females, choose mates based on certain desirable characteristics. ● Genetic drift: changes in allele frequencies due to random chance. ○ Genetic drift has a greater effect in small populations. ○ In large populations many more generations are required before an allele is eliminated or fixed. ○ Is a random process that doesn't select any particular allele, it can alter the frequencies of both beneficial and deleterious alleles. ○ Can promote neutral variation: changes in genes and proteins that don't have an effect on reproductive success. ■ Neutral theory of evolution: most variation in DNA sequences is due to the accumulation of neutral mutations that have attained high frequencies in a population via genetic drift. Explains genetic variation not affected by selection. ● Founder effect: when a small group of individuals separate from a larger population and establishes a colony in a new location. ● Bottleneck effect: the change in allele frequencies of the resulting population due to genetic drift. ○ The difference between the founder effect and bottleneck effect is that the founder effect occurs in a new location, although both effects are related to a reduction in population side. So for the bottleneck effect, the population is in the same location but some event was deleterious to the population. Memorize this equation: p +2pq+q =1 2 Criteria for hardy-winberg equilibrium ● No mutations ● No natural selection ● The population is so large that allele frequencies don't change ● No gene flow ● Random mating In hardy-weinberg population, p+q=1, q=?????? Why aren't natural populations n equilibrium?-- environments are always changing, always affecting it. Every population is subject to every criteria or at least one, subject to at least one will result in evolution to occur. Ch. 20 ● Subspecies: when two or more geographically restricted groups of the same species display one or more traits that are somewhat different but not enough to warrant their placement into different species. ● Ecotypes: many bacterial species are subdivided into this. ● The most commonly used characteristics for identifying species are: morphological traits, the ability to interbreed, molecular features, ecological factors and evolutionary relationships. ○ Morphological traits sometimes can be a flawed method of distinguishing species because some animals have extremely dissimilar appearances. ● Reproductive isolation: prevents one species from successfully interbreeding with other species. This affects its ability to interbreed, if it cannot breed with the subspecies then it is taken under consideration to be a new species. ● Molecular features refers to the DNA sequences in the genome of a species. The percent difference in DNA is debatable over how much % difference is needed to be considered a different species. ● Habitat differences are used to distinguish between species, because it affects the way the species can search for food for example. ● A species concept: is a way of defining the concept of a species and/or of providing an approach to distinguish one species from another. ○ Biological species concept: defines a species as a group of individuals whose members have the potential to interbreed with one another in nature to produce viable fertile offspring but cannot successfully interbreed with members of other species. ○ Evolutionary lineage concept: species should be defined based on the separate evolution of lineages. A lineage is a series of species that forms a line of descent, with each new species that direct result of speciation from an immediate ancestral species. ○ The ecological species concept: defines each species based on an ecological niche, which is the unique set of habitat resources that a species requires, as well as its influence on the environment and other species. ○ General lineage concept: each species is a population of an independently evolving lineage. Each species has evolved from a specific series of ancestors and, as a consequence, forms a group of organisms with a particular set of characteristics. ■ A population of an independently- evolving lineage ■ Derived from a specific set of ancestors ■ A group of organisms with a particular set of characteristics ● Reproductive isolating mechanisms: the mechanisms that prevent interbreeding between different species. ● Reproductive barriers are the consequences of genetic changes that occur because a species becomes adapted to its own particular environment. These mechanisms fall into two categories: ○ Prezygotic isolating mechanisms: which prevent the formation of a zygote ■ Habitat isolation: members of populations never come in contact with each other, may involve a geographic barrier. ■ Temporal isolation: species happen to reproduce at different times of the day or year. ■ Behavioral isolation: mating behavior and anatomy often play key roles in promoting reproductive isolation. (differences in songs birds sing which other birds recognize as a mating call among their own species). ■ Mechanical isolation: morphological features (size or incompatible genitalia) prevent two species from interbreeding. ■ Gametic isolation: two species may attempt to interbreed, but the gametes fail to unite in a successful fertilization event. ○ Postzygotic isolating mechanisms: which block the development of a viable and fertile individual after fertilization has taken place. ■ Hybrid inviability: this occurs when an egg of one species is fertilized by a sperm of another species, but the fertilized egg cannot develop past early embryonic stages. ■ Hybrid sterility: an interspecies hybrid may be viable but sterile. (mules). ■ Hybrid breakdown: hybrids may be viable and fertile, but the subsequent generations may harbor genetic abnormalities that are detrimental. Can be caused by changes in chromosome structure. ○ When two species do produce offspring, they are called an interspecies hybrid. 1. Speciation may occur due to abrupt events such as changes in the chromosome number that cause reproductive isolation. 2. Speciation may occur as a consequence of adaptation to different ecological niches. Reproductive isolation is a by- product of this adaptation (for sexually reproducing organisms). ● Cladogenesis: is the splitting or diverging of a population into two or more species. ○ Requires gene flow between populations to be interrupted. Does not exist ● Allopatric speciation: is the most prevalent way for cladogenesis to occur. Occurs when a population becomes isolated from other populations and evolves into one or more species. (geographic barrier). ● Adaptation to feeding can cause speciation as these adaptations can change physical appearances which benefit from one way of obtaining food. ● Sympathetic speciation: occurs when members of a species that are within the same range diverge into two or more different species even though there are no physical barriers to interbreeding. Although sympatric speciation is believed to be less common than allopatric speciation, particularly in animals, evolutionary biologists have discovered several ways in which it can occur. ○ Polyploidy: a genetic change that can cause immediate reproductive isolation in which an organism has more than two sets of chromosomes. ■ Occurs through complete nondisjunctional (when chromosomes don’t separate correctly) of chromosomes, which increases the number of chromosome sets in a given species. ■ Another mechanism leading to polyploidy is interspecies breeding. May produce an allodiploid: an organisms that has one set of chromosomes from two different species. ■ Haploid cells: have half the genes from each parent. ■ Sympatry: some members of a population may diverge and occupy different local environments that are continuous with each other. ● Development: refers to a series of changes in the state of a cell, tissue, organ, or organism. Development is the process that gives rise to structures and functions of living organisms. ● Evolutionary developmental biology (evo-devo): new field of biology that compares the development of different organisms in an attempt to understand ancestral relationships between organisms and the mechanisms that bring about evolutionary changes. Developmental homologies, particular steps of development. ○ Helps people discover genes that control development and how their roles in different species. ● Pattern formation: the interplay among cell division, cell migration, cell differentiation, and cell death. ● Heterochrony: refers to the evolutionary changes in the rate or timing of developmental events. ● Speciation: also can occur when a small population moves to a new location that is geographically separated from the original ○ Natural selection can rapidly alter the genetic composition of the population, leading to adaptation to the new environment ○ Adaptive radiation: a single species evolves into array of descendants that differ greatly in habitat, form or behavior. ● Hox genes are found in small animals ○ Variation in hox genes might have spawned the formation of many new body plans ○ Numbers and arrangements of hox genes varies among different types of animals ○ Increases in the number of hox genes might have led to greater complexity in body structure. ○ Are not only responsible for the complexity of the body but also where parts of the body go and what they do. *** when writing “hox” by hand it must be underlined, when typing, it must be italicized ● Modern taxonomy places species into progressively smaller hierarchical groups. ● Each group at any level is called a taxon. ● Domains; created by Carl Woese based on the information in the sequences of genes. ○ Under this system all life are grouped within three domains; bacteria, archea, Eukarya. ● In the taxonomy of eukaryotes, a supergroup lies between a domain and a kingdom. ● Taxonomy: science of describing, naming, & classifying living & extinct organisms ○ You have to publish a description of the differences between this new species and other plants that might be related; name has to be a unique binomen, with an order, domain, taxonomical hierarchy. ○ Which group? Family? ● Systematics: study of biodiversity among both extinct & extant organisms. Focused on evolutionary relationships. ● Taxonomic groups are based on hypotheses regarding evolutionary relationships. ● Phylogeny: the evolutionary history of an organism. ● "taxonomy reflects phylogeny"- the system is flexible because we are always learning more about evolutionary history We need a formal naming system because there are many types of organisms (level of biodiversity) ● Random names aren't helpful because they aren't informative & don't describe the relationship ● Vernacular names: vary in different languages & sometimes even within a country. ● The system of nomenclature (naming) developed by swedish naturalist Carolus Linnaeus is widely used ● A hierarchical (nested) system ● Latin or latinized names (although some greek roots are used ● A binomial system 2-part name ● Many of linaeus' names still stand today Taxonomy: ● Each group at any level in the hierarchy is called a taxon ● Highest level (largest category is domain [not part of linnaeus' original system]) ● Plural of genus=genera Domain Dear Kingdom King Phylum Philip Class Came Order Over Family For Genus Good Species Sex ● Binomial nomenclature ○ Genus name and species epithet; these make up the scientific name unique to each species ○ Genus name always capitalized ○ Species epithet never capitalized and can never stand alone ○ Both names italicized when hand written ○ Rules for naming established and regulated by international associations. ○ Cannot use abbreviation at the beginning of a sentence, only in the middle. ■ Incorrect: H. sapiens developed in Africa…. ■ Correct: It is hypothesized that H. sapiens developed in Africa. Phylogenetic trees: ● To propose a phylogeny, biologists use the tools of systematics ● Is an example of a model (a demonstration of a hypothesis) that describes phylogeny and shows the evolutionary relationships among various species ● New species can be formed by ○ Anagenesis (ana=continued change): single species evolves into a different species ○ Cladogeneis (clado= branching): a species diverges into two or more species ○ Nodes: are the meeting point of the fork showing where cladogenesis has occurred, diverging a species. ○ A clade consists of a common ancestral species and all of its descendants. Cladistics: ● One way to study & classify species based on phylogenies ● Cladistic approach discriminates among possible trees by considering the various possible pathways of changes ● Results in a particular type of phylogenetic tree called a cladogram- this is produced by a computer which analyzes data; generated by cladistics. ● Cladistics compares homologous traits, or characters, which might exist in more than one state. Ex: a front limb is a character may exist in many character states: arm, flipper, wing. ● Shared derived character ○ More than one taxa have a trait in common that originated in their most recent common ancestor ○ Basis of the cladistic approach: analyze many shared derived characters to deduce the pathway that gave rise to those taxa. ● A character that’s shared by two or more different taxa and inherited from ancestors older than their last common ancestor is called a shared primitive character. ● Characteristics of a cladogram: ○ Branch points: where 2 taxa differ in shared derived characters--are always dichotomous ○ Ingroup: the taxa being studied ○ Outgroup: a species or other taxon assumed to have diverged before the species in the ingroup, and outgroup will lack less than or equal to one shared derived characters found in the ingroup. ○ Based on the principle of parsimony (aka Occam's Razor). The characters on the cladogram, go on the right angles. The field of molecular systematics involves the analysis of genetic data, such as DNA sequences or amino acid sequences, to identify and study genetic homologies and propose phylogenetic trees. ● The principle of parsimony states that the preferred hypothesis is the one that is the simplest for all characters and their states
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