Bio 152 Study Guide
Bio 152 Study Guide Bio 152
Virginia Commonwealth University
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This 11 page Study Guide was uploaded by Vania Notetaker on Thursday September 15, 2016. The Study Guide belongs to Bio 152 at Virginia Commonwealth University taught by Alaina Campbell in Fall 2016. Since its upload, it has received 103 views. For similar materials see Introduction to Biological Science II in Biology at Virginia Commonwealth University.
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Date Created: 09/15/16
Bio. 152 Test 1 Study Guide Key Points// Terms // People Section 21.1 The difference in DNA sequence is the reason we have genetic variation. Population Genetics – The study of the differences in DNA sequences/ genetic variation of a population Population – interbreeding species located in the same geographical area Species - interbreeding individuals with different combinations of alleles in a gene pool Gene Pool – Total alleles of all individuals in a species Sources of Genetic Variation Mutation; creates new variation Somatic (in body tissues) Germ-line (reproductive cells, passed thru generations) Can be deleterious (harmful), neutral or advantageous (beneficial) Recombination; shuffles mutations, making new combo. of mutations Section 21.2 Measuring Genetic Variation Population genetics makes statements about the evolutionary process using patterns of genetic variation When understanding patterns in genetic variation allele frequencies are key. Allele frequencies – rate of appearance of alleles in a population Ways to Measure Genetic Variation Observable traits Guessing genotype & phenotype Gel electrophoresis; separation of segments of DNA according to size Proteins (enzymes) DNA sequencing Displaying # of times mutation occurs in population of n diploid individuals Section 21.3 Evolution – a change in a population’s genetic make up over time. Genetic variation must be in a population for evolution to happen **Populations evolve not individuals** The Hardy-Weinberg equilibrium describes when evolution doesn’t occur. Conditions of H-W equilibrium No diff. in the survival & reproductive success of individuals (no selection) No adding or taking from the population by migration No mutations The population has to be large enough to prevent sampling errors (genetic drifts) Random mating H-W equilibrium equation – used to predict genotype frequencies using allele frequencies and vice versa 2 2 P + 2pq + q = 1 P = Homozygous Dominate(AA) 2pq = Heterozygous(Aa) q = 2 Homozygous Recessive(aa) ** If you have p subtract it from 1 to get q and vice versa** If a population’s allele/genotype frequencies are not in equilibrium, evolutionary mechanisms are acting on the population and they’ve evolved If a population’s allele/genotype frequencies are in H-W equilibrium, evolutionary mechanisms are not acting on the population and they haven’t evolved Section 21.4 Natural selection leads to adaptation increasing the fit of organisms and their environment Population size, resources & competition determines who survives and leaves off-springs Darwin and Wallace figured out natural selection at the same time but credit it given to Darwin. Fitness- measure of representation of a genotype in next generation Mendel studied pea plants, with discrete traits meaning they had obvious alternatives As oppose to the traits studied by Mendel, most variations in populations are continuous meaning they occur across a spectrum not having an obvious alternative. Ronald Fisher combined Darwin’s natural selection and Mendel’s genetics to create a Modern Synthesis; evolution Natural select increases frequency of advantageous mutation & reduce frequency of deleterious mutations Natural Selection can create a fixation of beneficial alleles meaning the allele frequency will be 1. All individuals in the population are homologous to said alleles. Positive Selection – natural selection promoting the frequency favorable alleles Negative Selection – natural selection removing of the frequency of harmful alleles Balancing Selection – maintains two or more alleles in a population Heterozygous advantage - heterozygous fitness is greater then either homozygotes, insuring both alleles in population Consequences of Natural Selection Stabilizing selection; selection against extremes (keeps trait the same over time) Directional selection; selection against one of two extremes (change in trait over time) Disruptive selection; selection against the mean Artificial selection; removal of competitive element and selection of successful genotype by a breeder, common in agriculture Sexual Selection; promotion of traits pertaining to an individuals reproductive opportunity Section 21.5 Migration, mutation and genetic drift are non-adaptive parts of evolution Migration – transport of allele from one population to another; lowers genetic variation Homogenizing can decrease fitness Mutation – the changing of gene structure Beneficial mutations spread Neutral mutations stay in for thousand of years Harmful mutations are removed within a couple generations Mutation in somatic cells; not passed on Mutation in germ cells; passed on Without mutation, genetic variation wouldn’t occur; so there’d be no evolution ** Mutation is rare** Genetic Drift – when allele frequencies’ goes up or done simple by chances Bottleneck- population with only a few individuals Founder event population started but only a few Gene Flow - transfer of alleles from one population to another Section 21.6 Molecular evolution is change in DNA/amino acid sequences The amount of time species have been isolated is how long it’s been since they shared an ancestor. Molecular clock – the correlation between amounts of time two species have been isolated and how much genetic divergences are between them **Molecular clocks can be used to date evolutionary events ** **Histone Molecular clock is the slowest** (Histone is the protein DNA wraps around to make chromatin) Pseudogene – No longer functional gene Molecular clock clicks the fastest Mutation in itself is not important but paired with other evolutionary mechanisms is important Genetic drift- random changes in an allele freq. that’s usually happing in generations over time. Molecular clock- time scale for how a species is created Chapter 22 Species & Speciation Species - Ability to pass on your genes - Closed gene pool - Biological Species Concept (BSC) most common used def.: Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups Reproductive Isolation Pre—zygotic- prevent fertilization - Behavioral (Mating dance, bird singing) - Gametic isolation ( - Physical/mechanical incompatibly, lock and key - Time (temporal) and Space (ecological) Post- zygotic – prevent development into a fertile individual - Genetic incompatibility Problem with BSC - Hard to test - Morphospecies concept- members of the same species will look alike, with similar DNA - Cannot apply to asexual organisms - Cannot apply to extinct organisms - Ring species - Hybridizations Ecological Species Concepts (ESC)- ecological niche (ex. Bacteria & nutritional requirements) *Phylogenetic species concept (Evolutionary concept)(PSC)- members share a common ancestry - Apply to asexual species Speciation- the development of reproductively isolated populations resulting from the genetic divergence of separated populations **Partially reproductively isolated** Speciation from geographical separation *Most speciation *Subspecies 2 Processes for allopatric speciation - Dispersal; mainland population moves to an island population (Peripartric speciation) island pop. Has faster genetic divergence due to genetic drift & natural selection, adaptation to their new environment - Vicariance; change in the geography to spared a species **Research Darwin’s finches Speciation is a by-product of the genetic divergence of separated populations. - > If a population is split into two and aren’t able to interbreed different mutations will occur by chances in each of them. - > Then genetic drift and natural selection will make the two genes different over time. - >Then a change happens that make it so the two species once the same, can’t interbreed any more. - > This is speciation-> the development of reproductive isolation between populations Partially reproductively isolated- they are not yet separate species but the difference is great enough that the offspring they make have reduced fertility or viability compared to offspring of the same population. Allopatric speciation- this is speciation that comes from the geographical separation of populations. > Most species is thought to be allopatric Peripartric speciation – individual from a mainland population disperse to a new location remote from original population and evolve separately. > Island population Adaptive radiation- unusually fast evolutionary diversification in which natural selection makes adaptation and speciation happen faster. > Darwin’s finches Co-speciation- this is speciation that happens in response to speciation in another species at the same time. Gene flow makes it so a population can’t have genetic divergence. If natural selection acts strongly to counteract gene flow, disruptive selection (selection against the mean) happens stopping gene flow thus making sympatric (populations in the same geographical location) speciation possible. > Difficult to find evidence for it in nature, but not so much in plants Instantaneous speciation – This is hybridization between to species in which the offspring is reproductively isolated from both parents. > Can occur in single generations making it sympatric by definition. In hybridization cases number of chromosomes may change. > Tetrapliod – double diploid > Polyploidy – multiple chromosome sets Speciation can occur with or without natural selection > Genetic divergence between two populations can be because on genetic drift alone > Sympatric speciation requires disruptive natural selection > Allopatric speciation & adaptive radiation may happen because of natural selection Natural selection can enhance reproductive isolation Reinforcement – the process by which diverging populations undergo natural selection in favor of enhanced pre-zygotic isolation to prevent the production of less fit hybrid offspring. Chapter 23 Phylogeny – the history of decent with branching > Like genealogy that records our own family histories Nodes- represents last common ancestor Phylogenetic trees provide hypothesis of evolutionary relationships Systematics – the study of evolutionary and genetic relationships among organisms. Two disciplines in systematics > Phylogenetic > Taxonomy (the classification of organisms) Phylogenetic tree – a hypothesis about the evolutionary history of a species Tree of life is a phylogenetic tree for all species Informal name at the end of each branch represents a group of organism The search for sister groups lies at the heart of phylogenetics. Two species are closely related if they share a common ancestor (Node) Sister group- groups that are more closely related then any other group. > Phylogenetic hypothesis determines sister groups > Info. about evolutionary relationships lies in the order of nobes over time, not the order of groups along tips. A monophyletic group consists of a common ancestor and all its descendants Taxon- all species in some taxonomic entity under discussion Monophyletic- all members share a common ancestor not shared with any other species or group of species. Paraphyletic – includes some but not all descendants of a common ancestor -If to separate a group from the rest of a phylogenetic tree you need only one cut the group is monophyletic -If you need at least two the group is paraphyletic. -Groups that don’t include the last common ancestor are call polyphyletic **By removing some members of the group from a monophyletic group can provide a misleading sense of evolutionary history** Taxonomic classifications are information storage and retrieval system. Genus- grouping of closely related species Family – grouping of closely related genera Order- grouping of closely related families Class- grouping of closely related orders Phylum- grouping of closely related classes Kingdom- grouping of closely related phyla Domain- the three largest limb of the entire tree of life > Eukaryote > Archaea > Bacteria ** There is nothing particular about a group that makes it a class rather than an order** Therefore it’s not true that orders or classes are equivalent in any meaningful way **Sister groups are equivalent to on another in that they diverged from a single ancestor at a single point in time. ** Therefore the number of species means they’ve experienced different rates of speciation, extinction or both since divergence. Building a Phylogenetic Tree - Only some similarities between organisms are useful to determining common ancestor Homology by Common Descent Characters- anatomical, physiological, or molecular features that make up organisms. > Must vary among but not within species and have a genetic basis to be useful > Can be present or absent Character states- observed conditions of characters Reason character states can be similar - Character state was present in common ancestor of two groups and retained over time -- > Homologous- characters that are similar because of descent from a common ancestor - Character states independently evolved in the two groups as an adaptation to similar environments -- > Analogous- characters that are similar due to independent adaptation by different species ---- > Results of convergent evolution Shared derived characters enable biologist to reconstruct evolutionary history **Analogies are not useful in construction phylogenetic trees. ** **Unique character states to a species cant tell us anything about its sister group ** **Homologies present in all descents of a common ancestor aren’t helpful in sister group relationships either ** Synapomorphies – shared derived characters, homologies shared by some but not all members of a group under consideration Cladistics- phylogenetic reconstruction on the basis of synapomorphies Smallest Tree is often favored among multiple possible trees. ** Trees with fewer character changes are preferred to ones that require more because they provide the simplest explanation of the data** Parsimony – This is choosing the simpler (tree with fewest number of changes) of two or more hypothesis to account for a given set of observations. Each change = a mutation in an ancestral species Molecular Data complement comparative morphology in reconstructing phylogenetic history Tree construction relies on molecular data > The amino acids at particular positions in the primary structure of a protein can be used as characters > Nucleotides at specific positions along a strand of DNA **Molecular data doesn’t provide better records of history than comparative morphology** It is simply more detailed Morphological and molecular data are combined in analyses **GenBank **Encyclopedia of Life **The tree of life Phylogenetic trees can help solve practical problems Knowing the evolutionary history of something tells you what it is and how to handle it (i.e. Crop food diseases) Phylogenetic evidence provides a powerful tool for evolutionary analysis - Time-scales ranging from months to entire history of life, rise of epidemics to the origins of metabolic diversity Fossil contributions to phylogenetic trees +Time calibration +Not just fossilized organisms but trace and molecular fossils as well + Correlation between evolution and earth history + Records of extinct species ** Marine habitats are places that sedimentation, rather than erosion will take place, this is why record of marine life is more complete than that of living organisms in terrestrial ecosystems **
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