Bio Final Review.docx

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Health Sciences
Health Sciences 1001A/B
Shauna Burke

1 | P a g e Bio Midterm 2 Review Dr. Waugh Content Lec. 1 The Theory of Evolution – Key Concepts - What is a theory? - Historical development of evolutionary thought - Darwinian evolution - Road map for the evolution course What is a theory? common vernacular: an untested idea or opinion; speculation scientific definition: explanation of a set of natural phenomena, based upon proven or testable hypotheses and observations Examples of scientific theories: Natural Selection, Cell Theory, Big Bang Theory Early evolutionary thought static classification and characterization - Aristotle (384-322 BCE) & the Scala natura: The ladder of natural things (how close an organism is to perfection / gods) - Natural Theology (1700s) - Carl von Linne & the Linnean system (1707-78): Involved in the classification of species (based on the reproductive structure) - Developed the taxonomic Hierarchy Taxonomic hierarchy = Family – Orders – Classes – Phyla – Kingdoms - Domains, all life is divided into three domains - le Comte de Buffon (1707-1788) but…vestigial traits are traits that seem to be useless (lost throughout evolution) – Appendix Transformational theory of evolution Jean-Baptiste Lamarck (1744 – 1829) - Species evolve better fir their environment - Refer to diagram in notes 2 | P a g e Geological patterns Georges Cuvier (1769 – 1832) - Believed in fixity of species - Changes in fossil forms a result of repeated catastrophic events and new creations (catastrophism) Charles Lyell (1797 – 1875) - Natural agents currently at work have been at throughout earth’s history (uniformitarianism) - (earth has been gradually changing throughout time) Darwinian Evolution Charles Darwin (1809 – 1882) - Evolution by natural selection: species gradually change over time due to interactions between individuals’ traits and their environment Lec. 2 Natural Selection – Key Concepts - Investigating evolution by natural selection: Periwinkle snails simulation = the survival of the fittest ( red snails prevailed while the yellow snails were killed off quickly) - fitness (definition & calculations) - adaptation (definition & constraints) - microevolution (link to genetics & definition) - READING: Darwin’s observations and inferences Heritability of phenotype - Heritability of phenotype: proportion of phenotypic variation in a population due to variation in genes. - H= Vg/Vg+Ve - Where: H=variation in phenotype, Vg= Variation in genotype, Ve= Variation in environment - Problems with this correlation: doesn’t give you context of a cause (fixation WILL NOT equal causation) - Investigating Evolution by Natural Selection - Thickest shells survived and the thin shelled snails were killed off quickly Importance of Heritability of traits: - Heritable characteristics will produce NO change - Similar variation and mean - Average will not change and therefore evolution did not occur (this means heritable traits that include variation will cause natural selection) 3 | P a g e Evolution by natural selection - Variation is necessary for evolution - Heritability of variation is also necessary - Survival and reproduction my vary, according to the traits Natural Selection Definition: Defferential survival and reproduction of individuals in a population due to the current environmental fitness Evolution by natural selection is OBSERVALBLE Ex: - Antibiotic resistance in bacteria - Pesticide resistance in insects - Heavy metal tolerance in plants - Beak size in Darwin’s finches Fitness Definition: The degree to which an individual contributes offspring (genes / alleles) to future generations - Absolute fitness (W): number of offspring - Relative fitness (w): relative to others in the population BEST GENOTYPE ALWAYS HAS A RELATIVE FITNESS EQUAL TO 1 Adaptations Definition: traits that increase the probability that an individual with that trait will survive or reproduce in a particular environment Constraints on adaptations: - Available variation for selection to act upon - Changing environments over time - Conflict between selection pressures (trade-offs in fitness) (micro)Evolution Definition: small-scale changes in genetic make-up of a population - Refer to diagram in notes 4 | P a g e Lec. 3 Hardy-Weinberg Principle – Key Concepts - Investigating the Hardy-Weinberg Principle: Mendelian Pigs activity - review of frequencies and probabilities - Conclusions from simulation - Applying the Principle: Testing for departures from equilibrium - Artificial Selection: selective breading of animals or plants to ensure that desireable traits appear in succession generations Calculating proportions (aka. frequencies) - Ratio = 1:4 and 3:4 - Proportion = # of items in interest / #of items in total - Refer to notes for calculation examples What happens to the allele frequencies overtime? Genotypes- more heterozygotes Phenotypes- shifts to predominantly mixed characteristics The Hardy-Weinberg Principle Conclusions from simulation 1 Does knowing an allele is dominant tell you that it will be common? (or rare?) - Knowing in an allele is dominant DOES NOT tell us if it is common or rare - Knowing an allele is common DOES NOT tell us if it is dominant or recessive - Phenotype ratios for populations DO NOT produce even ratios (no 3:1, 1:1, 1:0) Conclusions from simulation 2 Allele frequencies stayed roughly the same overtime (consistent through the Hardy – Weinberg Pricniple) - Genotype frequencies (and therefore phenotype frequencies) in a population can be predicted from allele frequencies - Let p and q represent the allele frequencies What assumptions can be made from the Hardy-Weinberg Principle? 1. No selection – no phenotype had equal fitness 2. Random mating 3. No new mutations 4. No successful im/emigration – no gene flow 5. No random events (random fertilization) – no gene drift, assume large population Using Punnett Squares for Populations Allele frequencies give probabilities of gamete ‘genotypes’ Allele frequencies give expected offspring genotype frequencies based on probability - Refer to diagrams in notes Genotype frequencies of offspring: 2 - pxp = p - 2(pxq) = 2pq - qxq = q 2 Testing for departures from equilibrium - View example questions in notes 5 | P a g e Lec. 4 Evolutionary Mechanisms – Key Concepts - Origins of genetic variation - The ‘paradox’ of genetic variation - Mechanisms of evolution: - Mutation - Selection - Sampling drift - Gene flow - Non-random mating Where does genetic variation come from? - Mutations – translocations, deletions, insertions, duplications - Chromosomal Mutations – polyploidy, trisomy - Random Mating – crossing over (genetic recombination) - Random Fertilization – open population, independent assortment Source of new alleles Mutations Definition: Spontaneous and heritable change in DNA - Rare, random errors - Deleterious mutations - Advantageous mutations - THE ULTIMATE SOURCE OF GENETIC VARIATION How is so much variation possible if mutations are rare and usually harmful? - Homeotic genes regulate the expression of other genes - Mutations in regulatory genes for development can generate new body shapes - (mutations will change phenotypic structure) The paradox of genetic variation Shouldn’t selection reduce genetic variation? - Advantageous mutations should fix in a population (fixation) - Fix = only one allele present (the fixed one) - Genetic variation should be temporary Selection is not the only process that will generate evolution, and there is more than one type of selection. 6 | P a g e Selection HETEROZYGOTE ADVANTAGE – heterozygotes have higher fitness than either homozygote - Sickle-cell and malaria example Modes of Selection = Directional, Stabilizing, Disruptive Directional: - Fitness increases with phenotype value - Mean phenotype changes over time, variance is reduced (but may be changed) - Refer to notes for graphs Stabilizing - Intermediate phenotype has highest fitness - Mean phenotype is maintained and variance is reduced - Removing the extremes - Surviving alleles flourish - Variation is reduced, no change to the mean - Refer to notes for graphs Ex. Human birth weight - Historically, large babies and small babies had reduced survival relative to 7-8 lbs babies - Modern medicine has since reduced the variation in fitness Disruptive - Extreme phenotypes have highest fitness - Does not alter mean phenotype, variance increases (perhaps multi-modal distribution) - Both extremes have high fitness - More extreme phenotypes - Mean is still the same - Over more time, the intermediate will vanish - Refer to notes for graphs Ex. Bluegill sunfish male mating strategies - Large males defend territories, attracting females - Small males ‘sneak’ in and steal mating opportunities - Both large and small males have higher reproductive success than ‘medium’ males 7 | P a g e Sampling Drift (aka Genetic Drift) Definition: change in allele frequencies due to the effect of chance in small samples p=0.5=q= No change Random chance- can change the results of reproduction and therefore eliminate some genes from the gene pool - Unpredictable changes in the short term - Should cause fixation in the long term What can cause a change in genetic make-up due to sampling? 1. Random chance during reproduction 2. “Bottleneck events” that reproduce population size 3. “Founder effects” that create new populations from a small sample Bottleneck Events: Founder Effects: Gene flow Definition: the movement of alleles (closed vs. open) from one population to another - Tends to equalize allele frequencies among populations - Maintains genetic variation within populations - May oppose local selection pressures - Alleles that are missing will be introduced by gene flow, therefore maintaining genetic variation Non-random mating - Disrupts genotype frequencies, but not allele frequencies Definition: individuals select mates based in phenotype 1. Assertive mating - Like mates with like - Promotes inbreeding and homozygousity Inbreeding: mating between organisms that shares the same alleles 2. Disassortative mating - Opposites attract - Greater heterozygousity 8 | P a g e Lec. 5 Sexual Selection – Key Concepts - The evolution of sex - Sexual selection - intrasexual selection - intersexual selection - Parental Investment Why sex? – Creates Variation Disadvantages to sexual reproduction: - Could reduce fitness in offspring - Time consuming (could be collecting resources) - No guarantee of mate - Unsure about the partners contribution of alleles - STD / STI - Guard is let down while mating Advantages of sexual reproduction: The lottery model - Sexual reproduction increases the likelihood that some offspring will be appropriately equipped to survive - Increased likelihood that an offspring will be appropriately equipped means that there is an increase in fitness - Stable environments will not determine sexual or asexual reproduction. Sexual reproduction is more effective and more commonly used, given almost any environment. Sexual selection Sexual Dimorphism: physical differences between the two sexes - Differential reproductive success due to variation among individuals in success at getting mates Intrasexual selection: males are competing for mating opportunities Intersexual selection: females choose their mates IntRAsexual Selection Males monopolize access to females (get access to females and ensure that nobody else does) - Direct control of females - Control of a resource is important to females 9 | P a g e Methods of monopolization: - Combat traits- strength, size, weapons, and defensive attributes - Sperm competition - Infanticide – killing off of other males’ offspring IntERsexual Selection Females choose mates based on display of specific things This leads to: - Elaborate courtship / calls - ornamentation Ornamentation: things that attract the attention of females WHY? - Good gene hypothesis – the carrying of “good” or advantageous alleles - Acquisition of resources – gifts given to females in order to encourage reproduction - Sexy sons – something about a given trait that females want. Doesn’t necessarily mean that the trait is advantageous, it’s just desirable. Gender differences Why are females choosier? - Mothers make a larger “parental investment” in offspring than fathers - Male fitness is limited by mates - Females are motivated by quality, not quantity Lec. 6 Macroevolution: Speciation – Key Concepts - morphological species concept - biological species concept - reproductive isolation (reading) - mechanisms promoting speciation - reinforcement of accumulated differences Macroevolution Definition: the origin of higher order taxonomic groups (i.e. species and beyond) Brings together the concepts of: - common ancestry - decent with modification - speciation Speciation: the process of creating a new species over time through accumulation of micro-evolutionary changes Macro-evolution results from the accumulation of micro-evolutionary changes over time 10 | P a g e Morphological species concept (not black & white) Morphological similarities / differences are what quantify two organisms as “different species” - identified by morphological similarities - consistent with Linnean classification (reproductive structure) - occupy distinct clusters in phenotypic space - widely applicable BUT... some characteristics make it hard to determine whether organisms are of different species (this is what generates the “greyness”): - small organisms - phenotypic variation within the species - evolutionary history? Biological species concept Definition: groups generated from potentially or actually interbreeding organisms, making them reproductively isolated from other groups Reproductively isolated: something is preventing two populations from mixing gene pools through reproduction - Easy to apply this concept But... some problems with this concept include: - Asexual species? (incapable of inbreeding) - Natural reproduction? - Extinct species? Mechanisms promoting speciation 1. Allopatric speciation – barrier subdivides a population allowing for accumulation of differences a) Long distance dispersal (a portion of a population that is within the same species changes habitat and stays in this habitat for long periods of time) b) Vicariance = the formation of a geographic barrier, splitting a population in two (e.x. road or river) this is an example of directional selection FOUNDER EFFECT AND LONG DISTANCE DISPERSAL HAVE NO DIFFERENCE 2. Parapatric speciation – population spreads across a heterogeneous landscape - “para – parallel” - Parallel populations experiencing different environments - There is different selection in adjacent habitats 3. Sympatric speciation – divergence within a homogeneous environment May be caused by: a) Mutations (like polyploidy) – causing isolation - Malfunctions in reproductive processes b) Disruptive selection coupled with assortative mating NOT AS FREQUENT AS ALLOPATRIC OR PARAPATRIC SPECIATION 11 | P a g e Have they become different species? - We can make these assumptions when the two populations come together in secondary contact Secondary C
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