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Diversity of Life Biology 103 Instructor: Jim Driver Class Information Card Please take a few minutes to fill out a 3x5 card with the following information: • Name • Major • Class (Soph., Jr., etc) • Related courses taken • Career goals? • Expectations of this course • E-Mail address (optional) Course Business Instructor: Jim Driver ([email protected]) Required text: Biology, Campbell and Reese, 7th edition Diversity of Life is a continuation of Principles of Biology A comprehensive syllabus and lecture schedule will be provided This course will have four exams, one will be a takehome Course Business Classroom attendance is STRONGLY recommended Taking clear, concise lectures notes will help in this and future university classes Exam questions will come from the lecture notes. Use the textbook to better understand the materials covered in lecture, BUT……a thorough reading of the text will help in the future and may be enjoyable! How to study for my exams • Come to class • Take notes, pay attention to emphasis on topics or concepts • Use textbook to better understand notes • Know all terms in notes • If you have questions - ask during class or come see me during office hours Yes, life sure is diverse! Diversity of Life – Course Preview Biology of Life covered molecular biology, cell biology, and genetics. This course covers the rest! But seriously, topics we will cover include: How did life develop such diversity from its initial beginnings? How is life categorized? What are the hallmarks of the major life groupings? How does life interact on a local, regional, and planetary level? The molecular structure of DNA • Holds all the information to make a complex organism in 4 bases! Nucleus DNA Cell Nucleotide Figure 1.7 (a) DNA double helix. This model shows each atom in a segment of DNA.Made up of two long chains of building blocks called nucleotides, a DNA molecule takes the three-dimensional form of a double helix. A C T A T A C C G T A G T A (b) Single strand of DNA. These geometric shapes and letters are simple symbols for the nucleotides in a small section of one chain of a DNA molecule. Genetic information is encoded in specific sequences of the four types of nucleotides (their names are abbreviated here as A, T, C, and G). Diversity and Relationships • Carolus Linnaeus – taxonomy – How can we put all the organisms in the right boxes? – Developed binomial nomenclature (Genus species) – He classified similar species (by morphology) into increasingly general categories What is common thread in each grouping? Evolution and Diversity • Evolution accounts for life’s unity and diversity Darwin and “descent with modification” • Lamark’s theory of evolution – Use and disuse – Inheritance of acquired characteristics – Based on improvement of the individual during its life and transmission of the improvements to offspring What Lamarck thought… Darwinian Evolution • 1859 – On The Origin of Species By Means of Natural Selection (Alfred Russel Wallace also had same idea) – 2 main ideas • Evolution explains life’s unity and diversity • Natural selection is a cause of adaptive evolution • Remember: – Individuals survive and reproduce – Populations evolve and adapt Variation driven by random mutation and sexual recombination Overproduction Reproductive success Imagine an alternative scenario How did Darwin get to natural selection? Observations and inferences. • • • • • • • • Obs. #1 – all species have great potential fertility #2 – populations tend to remain stable #3 – resources are limited Inference #1 – overproduction leads to struggle for existence Obs. #4 – in a population, no two individuals are alike #5 variation is heritable Inf. #2 – individuals with inherited traits that best fit the environment will likely leave more offspring Inf. #3 – unequal survival and reproduction will lead to gradual change in a population, with favorable characteristics accumulating over the generations In other words…. • Natural selection is: – differential success in reproduction – an interaction between the environment and the variability in individuals making up the population • Natural selection leads to the adaptation of a population of organisms to their environment Evidence for natural selection • Antibiotic resistance in bacteria – Bacterial populations are not always clonal – Mutations in DNA during replication can lead to protein structure changes • Moth coloration in England – Pollution caused change in tree bark color – Some moths stood out leading to differential predation, changing population • Pesticide resistance in insect populations • Toxins in Newts Figure 22.12 The fittest survive and reproduce Understand: • Fitness –any heritable trait that increases relative reproductive success – Strictly dependent on the specific environment • Adaptation – refers to populations adapting to the environment, not the individual • Scientific Theory – useful, comprehensive, and well-supported explanation for a wide range of observations Understand: • Fitness –any heritable trait that increases relative reproductive success – Strictly dependent on the specific environment • Adaptation – refers to populations adapting to the environment, not the individual • Scientific Theory – useful, comprehensive, and well-supported explanation for a wide range of observations • Evolution in its strict meaning is a change in allele frequencies in a population over time…….But…… Time and scale of change in a population Evolution – change through time Macroevolution Speciation Microevolution Definitions • Microevolution – change in allele frequencies in population over time – Alleles - alternative versions of a gene that produce distinguishable phenotypic effects • Speciation – a population’s genetic divergence leads to reproductive isolation • Macroevolution – the level of change of life on the planet observed over geological time Understanding Evolution • Evidence indicates that all life on this planet is related. Eg. DNA-based • Later forms show a relationship to earlier forms based on common characteristics • Natural selection provides a mechanism to explain how these changes came about • Natural selection requires heritable variation in populations and conditions that favor one variant over another Evidence for evolution • Descent with modification can explain similarities in structures with different functions (homology) • Anatomical homologies Evidence of evolution • Descent with modification can explain similarities in structures with different functions (homology) • Anatomical homologies • Molecular homologies Biogeography • The geographic distribution of species • Closely related species inhabit same geographic region (common evolution) • But: – Same ecological niches in distant regions can be occupied by evolutionarily different species Biogeography • The geographic distribution of species • Closely related species inhabit the same geographic region • But: these ecological niches in distant regions can be occupied by evolutionarily different species • Darwin observed that many species are endemic Evolution of Populations Chapter 23 Population genetics • How do populations change (genetically) over time? • Gene pool – total of all genes in a population • Alleles – alternative forms of a gene – Remember in sexual spp. One gene from mom, one from dad Mendelian Genetics Review Mechanisms of Variation • Mutations – changes in nucleotide sequence of DNA – Only mutations gametes passed to offspring – Point mutations - single base change – Chromosomal mutations - large scale deletions, disruptions or rearrangements • Also gene duplication (eg detecting odors) – Mutation rates usually low in animals but much higher in prokaryotes (eg. HIV) Mechanisms of Variation • Sexual recombination – Rearranges alleles into new combinations each generation (review Chap. 13) – Remember, one chromosome of each pair from each parent – Do bacteria have sex? YES! • What does THAT look like? Sexual reproduction • Two parents give rise to offspring that have unique combinations of genes inherited from the two parents Crossing Over (Not on Exam) – Produces recombinant chromosomes with genes derived from two different parents Prophase I of meiosis Nonsister chromatids Tetrad Chiasma, site of crossing over Metaphase I Metaphase II Daughter cells Figure 13.11 Recombinant chromosomes Also Independent Assortment (not on exam) – Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs Key Maternal set of chromosomes Possibility 1 Possibility 2 Paternal set of chromosomes Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Figure 13.10 Combination 1 Combination 2 Combination 3 Combination 4 How populations change • Natural selection – Variants better suited to the environment tend to produce more offspring • Or → Genetic drift – population changes unexpectedly Genetic drift – unpredictable changes How populations change • Genetic drift can come about through: • Bottleneck effect; a few survivors • Founder Effect – A few individuals form an isolated population How populations change • Gene Flow – Movement of fertile individuals or gametes (eg. Pollen) into or out of a population • Egs, pollen, storms or tsunami’s etc. – Think humans and travel Adaptive Evolution and Variation • Genetic Variation can be: – Discrete characters (either/or) – Quantitative characters (vary along continuum) • Measuring variation – Average heterozygosity (eg. Fruit flies 1800 out of 13,000 gene loci,) – Nucleotide variability, in humans ~0.1% of DNA bases Variation between populations: - Geographic variation in a species can follow a cline (variation in trait that parallels environmental gradient) Fitness • – contribution individual makes to gene pool of next generation • Relative fitness – contribution of one genotype compared to alternative at same locus • based on reproductive success ONLY How does natural selection work? • Directional selection – Favors extremes at one end of distribution Modes of selection Natural Selection, again • Disruptive selection – Favors extremes at both ends of distribution Modes of selection Natural Selection, again • Stabilizing selection – Removes extremes and favors intermediates (most common type) Modes of selection Preserving variation • Most eukaryotes are diploid (2 copies of each chromosome/gene) • Homozygous – identical genes at a location • Heterozygous – different genes • Heterozygote advantage – sickle cell anemia How is it preserved? • Wouldn’t natural selection remove all unfavorable genotypes? • No, due to: – Recessive alleles – Heterozygote advantage (eg sickle cell) – Neutral variation (really neutral?) Hardy-Weinberg Theorem • Used to model non-evolving gene pools • Can be used to determine allele frequencies within a population – Or, what is happening to variation in a population • What is H-W good for? H-W Theorem • - frequencies of alleles and genotypes in gene pool remains constant from generation to generation if only Mendelian segregation and recombination of alleles happens • Requires: – Extremely large population size – No gene flow – No mutations – Random mating – No natural selection H-W and Sickle cell anemia (no math on exam) • Eg. In some populations the sickle cell allele is 20% of all hemoglobin alleles • H-W p2 + 2pq + q2 = 1 p = normal hemoglobin (0.8 of population) q = mutant hemoglobin (0.2 of population) p2 = (0.8)(0.8) = 0.64 or 64% of population q2 = (0.2)(0.2) = 0.04 or 4% population 2pq = 2(0.8)(0.2) = 0.32 or 32% of population What if? • Malaria eradicated – Change in natural selection? – Loss of heterozygote advantage? – Increase in gene flow? Sexual selection • Why sex anyway? – Lower reproduction rate than asexual – Provides variation for future selection/adaptation – Can provide short-term variation for disease resistance Sexual selection can lead to differences between sexes Sexual Dimorphism • If sexual characteristics increase mating success then benefit outweighs risk – “showy alleles” increase – Egs. Horns, coloration, displays The Evolution of Perfect Organisms: Why doesn’t it happen? • • • • • What is perfect? Evolution is limited by historical constraints Adaptations are often compromises Chance and natural selection interact Selection can only edit existing variation