Biology 111 Concepts of Biology Ch. 15 & 16
Biology 111 Concepts of Biology Ch. 15 & 16 BIOL 111
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This 12 page Class Notes was uploaded by Megan Giesler on Thursday April 7, 2016. The Class Notes belongs to BIOL 111 at University of North Dakota taught by Christopher Felege in Spring 2016. Since its upload, it has received 16 views. For similar materials see Concepts of Biology in Biological Sciences at University of North Dakota.
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Date Created: 04/07/16
Biology 111: Concepts of Biology Chapter 15 15.1 Natural Selection A process resulting in adaptation of a population to the biotic (living) and abiotic (nonliving) environments Darwin’s mechanism for evolution Most fit individuals become more prevalent in a population Leads to change in population over time Most fit individuals reproduce more than others because they are better adapted. Types of selection Most traits are polygenic and are controlled by more than one pair of alleles located at different gene loci. Such traits have a range of phenotypes resembling a bell-shaped curve. o Directional selection o Stabilizing selection o Disruptive selection Directional selection Occurs when an extreme phenotype is favored o On the far left or far right o Ex: The darker shell colors are favored and better suited for the environment so they survive and pass on their traits. The lighter shelled snails are now dying off. Distribution curve shifts in that direction Can occur when a population is adapting to a changing environment o Examples: Industrial melanism The prevalence of dark-colored varieties of animals (especially moths) in industrial areas where they are better camouflaged against predators than paler forms. Drug resistance in bacteria Pesticide resistance in insects Mosquitoes resistant to DDT Horses adapting from forest conditions to grassland conditions Stabilizing selection Occurs when an intermediate phenotype is favored o The medium colored shells are more likely to survive and reproduce. Extreme phenotypes selected against Individuals near the average are favored Most common form of selection because the average individual is well adapted to its environment Swiss starlings lay 4–5 eggs because this has the highest survival rate for young Disruptive selection 2 or more extreme phenotypes are favored over any intermediate phenotype o The medium colored shells are unfit for the environment and die at faster rates than the light and dark shells British land snails are found in fields and forests o In fields, thrushes eat the snails with dark shells o In forests, thrushes feeds mainly on snails with light shells Adaptations are not perfect Natural selection does not produce perfectly adapted organisms. Evolution is constrained by the available variations. Imperfections are common because of necessary compromises. o Success of humans attributed to freeing hands but walking upright puts stress on the spine Maintenance of variations A population always shows some genotypic variations. Population with limited variation may not be able to adapt to changing environmental conditions because they do not have another Forces promoting variation constantly at work o Mutations, recombination, independent assortment, and fertilization create new combinations o Gene flow The transfer of genes from one population to another o Natural selection favors certain phenotypes but others remain Diploidy and the heterozygote The heterozygote advantage Only alleles that are expressed are subject to natural selection. o Expressed = the cause in phenotypic differences Heterozygotes can protect recessive alleles. o Recessive allele might have greater fitness in a changing environment Balanced polymorphism o When natural selection favors the ratio of two or more phenotypes in generation after generation o Sickle-cell disease Sickle-cell disease S S Individuals with sickle cell disease Hb HB Tend to die early A S Heterozygotes carry the trait Hb HB Red blood cells only sickle at low oxygen concentrations A A Ordinarily the normal genotype is most fit Hb HB Recessive allele Hb has a higher frequency in regions in Africa where malaria is present Malaria is caused by parasite that invades and destroys normal red blood cells Parasite unable to live in heterozygote red blood cells Each of the homozygotes is selected against but is maintained because the heterozygote is favored in those parts of Africa 15.2 Microevolution Microevolution is a small measurable evolutionary changes within a population from generation to generation Individuals do not evolve. As evolution occurs, genetic and phenotypic changes occur within a population o A population is all the members of a single species occupying a particular area at the same time and reproducing with one another. Darwin stressed that members of a population vary. o Each gene in sexually reproducing organisms has many alleles. Reshuffling of alleles during sexual reproduction can result in a range of phenotypes. Evolution in a genetic context Gene pool o The various alleles at all the gene loci in all individuals of a population o Described in terms of genotype and allele frequency Peppered moth color example o D = dark color d = light color o From the genotype frequencies, you can calculate the allele frequencies of a population. Assuming random mating, we can use allele frequencies (gamete frequencies) to calculate the ratio of genotypes in the next generation using a Punnett square. Allele frequencies remain the same o Sexual reproduction alone does not bring about a change in allele frequencies Dominance does not cause an allele to become a common allele. G. H. Hardy and W. Weinberg used the binomial equation to calculate the genotypic and allele frequencies of a population. p = frequency of dominant allele q = frequency of recessive allele p + 2pq + q = 1 *There is another section of notes I have taken that provide more information on this if needed. Hardy-Weinberg principle states that an equilibrium of allele frequencies in a gene pool will remain in equilibrium as long as 5 conditions are met: o No mutations o No gene flow o Random mating o No genetic drift o No selection These conditions are rarely if ever met Allele frequencies do change from one generation to the next Therefore microevolution occurs Hardy-Weinberg equation is significant because it tells us what factors cause evolution Evolution can be detected and measured by noting the amount of deviation from a Hardy-Weinberg equilibrium of allele frequencies in the gene pool of a population Industrial melanism example Increase in the frequency of a dark phenotype due to pollution Before soot darkened tree trunks, light moths escaped detection of birds and were more common. After the advent of industry, dark-colored moths became more common as light moths were detected and eaten. Natural selection can occur within a short time frame. Change in gene pool frequencies occurs as microevolution occurs Causes of microevolution Any condition that deviates from the list of conditions for allelelic equilibrium causes evolutionary change o Genetic mutation o Gene flow o Nonrandom mating o Genetic drift o Natural selection Genetic mutations One major source for allele differences Without mutation there would be no new variations among members of a population for natural selection to act on Adaptive value of mutation depends on current conditions Gene flow Also called gene migration Movement of alleles among populations by migration of breeding individuals Can increase variation within a population by introducing novel alleles from another population Continued gene flow reduces differences among populations o Can prevent speciation * Here is a short video if you need more explanation as to what gene flow is: https://www.youtube.com/watch?v=H2BJN__Jtzk Nonrandom mating Selection of mate according to genotype or phenotype (not chance) Assortative mating o Tend to mate with individuals with the same phenotype o Homozygotes increase in frequency Sexual selection o Favors characteristics that increase the likelihood of obtaining mates Genetic drift Refers to changes in the allele frequencies of a gene pool due to chance Allele frequencies “drift” over time depending on which members die, survive, or reproduce More likely in small populations More likely to lose rare alleles Two types o Bottleneck effect o Founder effect Bottleneck effect Species suffers a near extinction and only a few survivors go on to produce the next generation o This can happen for several reasons one example is a natural disaster Founder effect Rare alleles occur at a higher frequency in a population isolated from the general population. Alleles carried by founders are dictated by chance alone. Amish—1 in 14 carries recessive allele for unusual form of dwarfism compared to 1 in 1000 in most populations * Here is a video on genetic drift, bottleneck, and founder effect if you need more explanation: https://www.youtube.com/watch?v=Q6JEA2olNts&nohtml5=False Biology 111: Concepts of Biology Chapter 16 16.1Speciation and Macroevolution Macroevolution Changes in a population over a very long period of time Problem with this is that it is a relative term. o For example, people take roughly 20 years to reproduce, and bacteria take 20 minutes. So what is a “really long time”? Always remember that evolution is descent with modification, or change in allele frequency. The question with macroevolution becomes whether or not those changes make something a new species, and this can be through branching, or non-branching evolution So what is a species? A Species is a group of organisms living in the same are who can reproduce and make viable offspring Speciation o Splitting of one species into two or more new species Species originate, adapt to their environment, and then may become extinct Biological species concept Members of a species o Interbreed o Have a shared gene pool o Each species reproductively isolated from every other species Not based on appearance Gene flow occurs between populations of a species but not between populations of different species. o Flycatchers look similar but are different species. o Humans can look very different but are the same species. The biological species concept only applies to living sexually reproducing organisms. Other definitions of species o Category of classification below rank of genus o Species in the same genus share a recent common ancestor. The reason for needing these other definitions is because of species like bacteria, or even some plants, who do not reproduce sexually. Reproductive barriers Isolating mechanisms that prevent successful reproduction (producing fertile offspring) from occurring Prezygotic - Before formation of a zygote o Habitat isolation Two populations occupy different habitats o Temporal isolation Two populations mate at different times of the day, month, season, or year o Behavioral isolation Sexual competition limits chance of mating o Mechanical isolation Sex organs are incompatible o Gamete isolation Sperm cannot fertilize egg Postzygotic - After formation of a zygote o Zygote mortality The hybrid zygote is not viable so it dies o Hybrid sterility The hybrid is infertile Ex: Donkey and horse mate to make a mule but the mule cannot reproduce o F 2itness If hybrids are able to reproduce their offspring is unable to Models of speciation Allopatric o Speciation model based on geographic isolation Sympatric o Population develops into two or more reproductively isolated groups without prior geographic isolation o Found among plants due to polyploidy Adaptive radiation New species evolve from a single ancestral species. Galápagos Islands finches adapted to eating different types of food Populations on different islands subjected to founder effect involving genetic drift, genetic mutations, and the process of natural selection Each population became adapted to a particular habitat on its island. New finch species do not interbreed. 16.2 The Fossil Record Fossils o Traces and remains of past life or any other direct evidence of past life Paleontology o Science of discovering and studying the fossil record and making decisions about the history of species Geological timescale Humans have only been around 0.04% of the history of life. Pace of speciation Gradualistic model o Darwin thought evolutionary changes occurred gradually o Often shows evolutionary history as an evolutionary tree o Difficult to indicate when speciation has occurred because of transitional links Punctuated equilibrium o Period of equilibrium (no change) is interrupted by speciation o Transitional links less likely to form fossils and less likely to be found Differences between models are subtle o “Sudden” in geological time may be thousands of years. Mass extinctions of species Disappearance of a large number of species or a higher taxonomic group within a relatively short period of time Occurrence of 5 mass extinctions o End of Ordovician, Devonian, Permian, Triassic, and Cretaceous periods o Significant mammalian extinction at the end of the Pleistocene epoch Many factors contribute o Continental drift Movement of continents can lead to massive habitat changes o Impact of meteorites Proposed as primary cause of Cretaceous extinction 16.3 Systematics Study of evolutionary history of life on Earth One goal is to determine phylogeny o Evolutionary history of a group of organisms Taxonomy o Identifying, naming, and classifying organisms Linnean classification Binomial system o Genus and specific epithet Naming rules o Genus capitalized, italics, and can be abbreviated o Ex: Cypripedium acaule = C. acuale o Latin to remove confusion based on common names Hierarchical system o The higher the category, the more inclusive Phylogenetic trees o Diagram that indicates common ancestors and lines of descent (lineages) o Common ancestor at the base of the tree has traits shared by all the other groups in the tree Quick Youtube video to help understand phylogenitic trees – https://www.youtube.com/watch?v=7WWGDKEqlyc A video relating family trees and cladograms to phylogenetic trees (pretty darn good) – http://study.com/academy/lesson/cladograms- and-phylogenic-trees-evolution-classifiations.html Tracing phylogeny Uses a multitude of data to discover evolutionary relationships between species Morphological data o Homologous structures are related to each other through common descent Ex: Forelimbs of vertebrates o Sometimes difficult due to convergent evolution Acquisition of the same or similar traits in distantly related lines due to adaptations to the same environment Analogous structures Same function but no recent common ancestor Molecular data o The more closely related species are, the more similar their DNA o Ribosomal RNA changes little and can be a reliable indicator Cladistics Way to trace evolutionary history of a group by using shared traits derived from a common ancestor to determine relationships Cladogram o Depicts evolutionary history of a group based on available data o Outgroup Not part of the group being studied o Ingroup Part of the group being studied o Parsimony least number of assumptions is the most probable Construct cladogram that minimizes number of assumed evolutionary changes o Shared derived traits Homologies shared by only certain species of the study group o Ancestral trait Present in common ancestor to ingroup and outgroup Linnean classification versus cladistics Linnean classification places birds in their own group but cladistics places them in a clade with crocodiles. May modify Linnean classification or construct an entirely different system 3 domain system o 5-kingdom system changed based on rRNA sequencing data o Domain Bacteria Arose first, prokaryotic cells o Domain Archaea Arose next, also prokaryotic cells o Domain Eukarya Last to evolve, eukaryotic cells Kingdoms for protists, plants, fungi and animals
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