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Chapter 13

by: Alexa Rosenfeld

Chapter 13 BIOL 1030-003

Alexa Rosenfeld
General Biology I
Kristi J. Whitehead

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General Biology I
Kristi J. Whitehead
Class Notes
Biology 1030, Bio, BIO 1030, Dr. Whitehead, Clemson, Clemson University, CU
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This 0 page Class Notes was uploaded by Alexa Rosenfeld on Tuesday November 17, 2015. The Class Notes belongs to BIOL 1030-003 at Clemson University taught by Kristi J. Whitehead in Fall 2015. Since its upload, it has received 105 views. For similar materials see General Biology I in Biology at Clemson University.


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Date Created: 11/17/15
Chapter 13 How Populations Evolve SECTIONS 1311317 Darwin was not the first to believe that populations evolve over time Passive process through which populations change Blue footed birdwebbed feet aquatic birds large tail that serves as a brake these characteristics help them in the environment that they live in Adaptations that an organisms acquire are only good for the pressures that the environment they live in and not for a different environment that they are not used to Adaptations are inherited traits that provide an advantage in terms of survival reproduction but it is only based on the selective pressure for a particular environment Sections 131136 Darwin s Theory of Evolution Greek Philosophers 0 Life forms changed over time but they didn t know why or how they did so Aristotle 0 What you see is what you get 0 Everything is created in a perfect form 0 Not the scientific theory of evolution Fossils 0 Controversial 0 Shows us that things have changed 0 Millions of years old and show that things are different than what we have today Lamarck 0 Had an idea of why and how they would change 0 Disagreed with Darwin 0 Organisms change based on use and disuse I EX giraffes had a short neck but with Lamarck s theories he believes that giraffes necks stretched longer and longer so that they can reach leaves on trees The parts of your body that you use more will become stronger and the ones you don t will eventually weaken The Voyage Charles Darwin Made this trip in his mid 20 s and came to the conclusion that the earth was much older than we thought it was and its not just old but it has been changing over time Figure 131 A Page 256 The pressures and environments that living organisms live in are changing Geography seemed to matter also Tortoise Figure 131 C Page 257 I Were at the brink of extinction 15 they could find and were isolated and breadedover 1500 baby tortoises have been breaded within 45 years from this I Iguana 0 131 B Darwin s Writings I 1859 published On the Origin of Species by Means of Natural Selection 0 2 main points 0 Organisms change and The changes help them survive better in their environments I There is variations in a population some good and some bad I Good variations adaptationsorganisms survive better with these variations and they reproduce at higher rates I Populations always overs produce based on what the environment can support which then leads to competition 0 If there is competition and one variation is surviving and reproducing better they will win and their rates will increase within the population I Accumulation of adaptations to allow organisms to fit in certain environments 0 The adaptations accumulate through inheritance and are being modified as they descend 0 Natural selection is the process through which evolution happens Darwin s Theory of Evolution 0 Based it on 0 Existing organisms O Ancestral organisms 0 Natural selection 0 Artificial selection humans put selective pressures on selected things to provide advantages I Ex seedless watermelon dog breeding pigeon breeding 39 Figure 136 Page 262 Natural Selection I Observations 0 There are many variations that exist in a population 0 Species can produce more offspring than an environment can support I Connections between observations 0 Antibiotic resistance 0 Idea that the competition will eventually select what will hae the particular adaptation 0 Important points 0 Over time you will see more and more individuals with the same adaptation O Populations evolve not individuals Only talking about heritable factors 0 Evolution is not goal directed it is not trying to lead to perfection it is a response to reproductive rates with certain environmental pressures O Environments are different so you can see the results of the different environmental pressures O Camou age O 0 Darwin s Finches 0 Single ancestral finch but due to different pressures in different parts of the islands there are now over 30 species 0 Pesticides 0 The pesticide will cause the death to all of the insects that are not resistant to then move to an environment that are all resistant to the pesticide 0 Figure 137 Page 263 0 Fossils 0 Gives a general time line 0 Looking at where we find fossils relative to each other deeper older closer younger Rare conditions in which fossils form Only certain types of artifacts can form fossils Fossils can be destroyed Fossil record isn t perfect Figure 132 B Page 258 Combination of fossil records and molecular biologists that come together with their hypotheses Decent of the whale from different hypotheses Figure 133B Page 259 Fossil record Shows the order in which organisms existed Based on certain techniques it can give us a relative time Oldest prokaryotic organisms 39 35 billion years old I Oldest unicellular eukaryotic organisms after a billion years I Oldest multicellular eukaryotic organisms after a billion years 000000 00000 Other Evidence 0 Biogeography O Decent from a common ancestor in a similar geographical area 0 Comparative anatomy 0 Bone structure 0 Figure 134 A Page 260 O Homology is when we have structural similarities based on common ancestry 0 Figure 134 B Page 260 0 Molecular biology 0 DNA amino acid protein sequences 0 Each time you have a branch point you have a common ancestor 0 Figure 135 Page 261 0 Molecular biologists do the same thing but instead of looking at physical characteristics they look at DNA Sections 13713 10 The Evolution of Populations I The genetics of the population is changing over time and that is what evolution looks at Populations Evolve 0 Population is a group of individuals in the same species 0 Isolated I When isolated all of the breeding happens within the population I Some situations breeding could happen across populations 0 Gene pool all of the genes and all of the versions of those genes alleles in a population 0 Microevolution The allele frequencies are changing looking at it on a genetic scale Genetic Variation in a Population 0 Darwin knew this but what he could not explain is why there was variation and he didn t know how they were passed from generation to generation I Comes from alleles different versions and is passed on to chromosomal inheritance 0 Figure 138 Page 264 0 Mutations 0 Stable changes in DNA sequence 0 Something has changed and the change is passed on at least for several generations get alleles Tend to be more harmful than beneficial Rare for a beneficial mutation to come about due to mutations from the past 0 Chromosomal duplications is where a portion is copied and moved having two of the same region of a chromosome I Could lead to the production of better proteins and the expansion I Mouse has over 1300 genes that help them smell and they are derivatives 00 of the one ancestral gene that was followed by mutational events Sexual reproduction O Crossing over 0 Metaphase I 0 Random fertilization HardyWeinberg Equation 0 How do we know if something is evolving 0 Principle 0 TWO scientists interested in Whether or not a population was evolving during a certain time A population Where there is sexual reproduction When dealing With diploids the norm is that the gene pool Will stay the same unless there is some outside pressure causing it to shift What is in the population When you study it Complete dominance I Nonwebbed WW WW I Webbing WW homozygous recessive 39 Figure 1310 A Page 266 I Only applies to diploid organisms I 500 organisms 1000 chromosomes I Allele frequencies 0 HOW many dominant Recessive 0 640 W 0 40 WW 0 160 W o 160 W 39 Figure 1310 B Page 266 I In order to tell if the population is evolving you have to look at the next generation genotypic and allele frequencies if there is no evolution occurring I If you don t find exactly this your population is evolving I Be able to tell genotypic frequencies and allele frequencies and have an appreciation that if it changes evolution is happening I Figure 1310 C Page 266 0 In order to maintain O O 0 Large population No gene owneW alleles coming into or leaving the population no gene ow means nobody goes anyWhere No mutation Random mating no preference for particular traits in terms of traits and mating completely random no selection No natural selection can t have any type of outside force that puts pressure on any members of the population If all are true the population is not evolving and Will be in the equilibrium 0 HOW to disrupt O O O 0 Small populationsingle member undergoing change can have a major impact Gene ow members can come in and leave population Mutations always have a chance to be advantageous Nonrandom mating some sort of selection 0 Natural selection something is providing pressure to make them survive and reproduce better Sections 13111317 Mechanisms of Microevolution 0 Changes within the allele frequencies in a gene pool 0 Changes in the gene pool are due to O Mutations can be advantageous but they usually are not and it is random so the contribution is rare and small Nonrandom mating does not tend to alter allele frequencies 3 main causes I Natural selection 0 Competition 0 Some are better at reproducing than others because of variation 0 Most consistent effect because there is variation that directly impacts reproductive success 39 Genetic drift 0 Change due to chance 0 2 types 0 Bottleneck Effect Some type of natural disaster effects the alleles and the total size of the population is cut way down and what is remaining in the small population you do not have the same distribution of alleles as you did in the initial population Can lose alleles and the frequencies can change Figure 1312 A Page 268 O Founder Effect Not a natural disaster Large population with different alleles and a portion is going to leave the original population and found a new population The likelihood of the allele frequencies being the same is very small Number of cases in the human population 0 Colonies 0 When you have a smaller population changes matter way more than in a larger population 39 Gene ow 0 Gene ow between the population where members from one population is leaving the other and vice versa 0 Reduces differences 0 Over time the population can become extremely different but with gene ow that likelihood is very small Natural selection 0 Natural selection is the only one that consistently allows for alleles to be better at competing in the environment I The others are totally due to chance and there is not a guarantee that the outcome will be beneficial I Some variations are going to be favored over others because of the pressures from the environment with a sorting process that is also blended with chance I Relates to relative fitness 0 Due to the variation some organisms are going to reproduce more than others 0 Survival of the fittest is that certain alleles will survive from generation to generation and some will die out 0 3 ways it can impact variation phenotype allows to interact I Stabilizing 0 The intermediate phenotypes are the ones that are most well adapted and the extremes are the least fit and are selected against making the alleles lost from the population I Directional 0 There is some selected pressure that favors over another population 0 Darker colored mice over the light colored mice I Disruptive 0 Either extreme is selected for and the intermediate is selected against 0 Figure 1314 Page 270 Sexual Selection 0 Form of natural selection 0 In a lot of animal species there are phenotypic differences between males and females 0 Sexual dimorphism I Some characteristics lead to a larger likelihood for mating O Intrasexual selection I Within a gender I Males will fight with each other for the female 39 Figure 1315 B Page 271 O Intersexual selection I Selection happens between the genders I One of the genders is ashier than the other gender I Darwin thought it was fascinating birds I Figure 1315 A Page 271


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