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Chapter Population Genetics OBJECTIVES Relate the study of genetics to that of population genetics and discuss factors that can affect genepool equilibrium Explain the HardyWeinberg model Discuss evolution through natural selection Explain genetic drift and contrast its effects on large and small populations. Discuss the role of quantitative traits in microevolution. Population Genetics Recall variation among individuals allows populations to adapt to new environmental conditions or to be selectively bred for desirable traits. Types of Evolution Microevolution change within a species. Occurs over dozens or hundreds of generations Macroevolution Much longer time period. Results in a new species A More Precise Definition Microevolution is a change in the genetic composition of populations. Studied by population geneticists. Gene pool All alleles in a population of organisms. Allele frequency Percentage of a particular allele in one population. Ex In a population of pea plants that are all homozygous for purple flowers, allele freq. for purple flowers is A change in an allele frequency is an indication of evolutionary change. Allele Frequencies within Beetle Population Polymorphic Populations Have or more alleles for a particular trait. Ex humans are polymorphic for blood type. Ex apple trees are polymorphic for fruit color. Hidden Genetic Variations Mutation in noncoding regions of DNA Silent mutations code for the same amino acid Unseen polymorphisms The HardyWeinberg Model An idealized mathematical model of gene pools. Mathematician Godfrey H. Hardy Physicist Wilhelm Weinberg Use allele freq. to calculate genotype freq. Allele frequency p and q, p q In the next generation p pq q Homozygous p p Heterozygous pq Homozygous q q HardyWeinberg Equilibrium Allele and genotype frequency will stay constant in the absence of disturbing influences. p pq q HardyWeinberg Model Makes some assumptions about the population. No disturbing influences. random mating no mutation the alleles dont change no migration or emigration infinitely large population size no selective pressure for or against any traits. HardyWeinberg Equilibrium Predictions of the model . Predicts allelic and genotypic frequencies . Genetic variation remains in the population unless selective pressures Good news for Darwin Assumed blending inheritance. Genetic equilibrium a constant state of allele frequency The following conditions must be met in order that genetic equilibrium not be disrupted. No natural selection Random mating No migration No mutation Large population size Note does not occur in nature. So, why use HardyWeinberg model Quick Quiz . Would a change in allele frequencies be more likely to produce microevolution or macroevolution . What is the difference between gene pools and allele frequencies . Why does the concept of gene pools apply to populations but not to species A Normal Distribution results from Stabilizing Selection Natural selection that favors average individuals in a population. Normal Distribution IQ Females only mate with males with the largest tails. Over time, tails have gotten continually larger due to this selective pressure. Directional Selection in Peacocks Peppered Moths color variations allele frequency was light, dark allele frequency dark, light Disruptive Selection Natural selection that favors either extreme trait. Disruptive Selection in Snails Limpets with lightcolored shells blend in with light rocks and sand. Dark shells blend in with dark rocks. Limpets with mediumcolored shells are easily seen on both rocks and eaten by birds. Disruptive Selection in Spiders When spiders are small, they are not as easily seen by predators. When spiders are large, they are often too big to be eaten. Spiders in the middle are the most vulnerable to predators. Other Factors Affecting Gene Pools Gene Flow Migration to a new population, organism may bring new alleles with it. Mutation If beneficial, will be favored by natural selection and gradually increase in frequency Genetic Drift Spontaneous changes in allele frequencies. Small populations only. Other Factors Affecting Gene Pools Inbreeding Gradual increase of homozygotes. Ex California Condor Population bottleneck Population size reduced for a few generations. Inbreeding results. Ex Buffalo in the s. Inbreeding increases frequency of harmful recessive alleles. Leads to Inbreeding Depression reduced fertility and survival. Did you know The average human is estimated to have alleles that would be lethal if they were homozygous In inbred populations, inheriting of these alleles is more likely. BSCS Biology A Molecular Approach Population Genetics CONCEPT REVIEW Evolution results from a disruption in genetic equilibrium. The normal distribution of variations in a population can be changed by natural selection, gene flow, mutations, and genetic drift Chapter Diversity and Variation Outcomes Explain homology and give examples of homologous structure Describe how the general characteristics of the kingdoms differ. The or Kingdoms Archaebacteria Eubacteria Protista Fungi Plantae Animalia Bacteria/monera Bacteria Prokaryotes First organisms to evolve Protista Earliest eukaryotes. Usually single celled. No organ systems Nucleus developed Mitochondria, flagellates, and plastids became incorporated. Ex amoeba, paramecium, algae Fungi Usually multicellular except yeast Eukaryotic Heterotrophs Evolved from funguslike protists slime molds Ex mushroom, mold, yeast Plantae Multicellular, with complex body systems roots, stem, leaves Autotrophs Eukaryotes Evolved from photosynthetic bacteria Ex Flowering plants, Conifer, Mosses, Ferns Animalia Multicellular with complex systems Heterotrophic Eukaryotic Ex Fish, Amphibian, Reptile, Bird, Mammal There are still lobefinned fish today called mudskippers. species have been identified. Unlike those we evolved from, most of todays species have only appendages front lobefins Fish to Amphibians Reptiles to Birds Reptiles to Birds Evolution of Mammals Eventually, some mammals returned to the water. Todays whales had an ancestor similar to a wolf. Chapter Changes in Species Outcomes Cite evidence from fossils, ecology, and homologies that support the theory of evolution Discuss the genetic and molecular evidence for evolution Discuss isolation mechanisms that can cause speciation Describe the patterns in evolution such as punctuated equilibrium Fossils as evidence of evolution Fossils are the preserved remains or imprints of ancient organisms. Fossils the only evidence we have that tells us directly about life in the past. This extinct dragonfly had a wingspan of feet Life first appeared on earth more than billion years ago. Fossils of algae and diatoms Millions of now extinct creatures lived on earth before humans came along. Some fossils are the actual preserved remains of the organism SoftTissue Fossils Ice in the Arctic has preserved some fossils for ,s of years. In a wooly mammoth was discovered intact. Can it be revived by crossing with an elephant Different s of chromosomes and , but similar DNA. Scientists have found , species of extinct orgnisms Estimate that only in , have been found. Evolution of the Horse In these pictures, there appears to be a straight line progression from the first horse ancetor to the modern horse species. Such a progression implies an evolutionary goal, since there is a trend toward larger body size and fewer toes. Evolution of the Horse However, evolution rarely follows a straight line to a goal. Remember, There are no goals in evolution Evidence for Evolution Body Structures homologous vestigial analogous Homologous Structures Traits that are similar in different species because they share a common ancestor. Note how the bones have adapted to different niches This is evidence of a common ancestor. Vestigal Structures No longer used. The Human Tailbone This is evidence that humans evolved from an ancestor that had a tail. Vestigal Organ human appendix appendix A whale has a pelvic bone too, and tiny leg bones. Analogous Structures structures that are similar in function but are not inherited from a common ancestor. NOTE Analogous structures indicate that organisms are not related. Embryology is also used as Evidence of Evolution Similar development of the embryo is evidence of a common ancestor All three embryos have gill pouches in the folds of the neck. All three have tails. Perhaps the clearest biochemical evidence of the common origin of living things is the genetic code. The same nitrogen bases of adenine, thymine, guanine, and cytosine exist in every form of life. In addition, the genetic code itself the codons for the amino acids is almost universal. The genetic code is the same in every known organism. Every organism uses the same base codes for amino acids Degree of Relatedness Can be determined by Amino acid sequence Homologous proteins Nucleotide sequence Homologous genes. More Genetic Evidence Pseudogenes Gene duplication produces multiple copies of DNA sequences. Pseudogenes gene copies that dont function, so arent subject to natural selection. Mutations occur unchecked. According to natural selection, these noncoding sections should accumulate mutations faster than functional genes and they do Amino Acid Sequence Can be used to determine relatedness How fast do evolutionary changes take place Based upon Darwins theory it has long been believed that evolutionary changes were slow and gradual Gradualism. scientists Stephen Jay Gould and Niles Eldridge advanced a different explanation about the rate of evolution called Punctuated Equilibrium Punctuated Equilibrium populations remain genetically stable for long periods of time, interrupted by brief periods of rapid change. sudden changes in the environment increased mutation rate. stasis Speciation is the evolution of one or more species from a single common ancestor species. Patterns of Evolution How do species remain separate Potential mates do not meet. Grizzly and Polar bears. Potential mates meet but do not breed. Nocturnal and diurnal birds. Leopard frog populations that breed during different months. Potential mates meet and breed, but do not produce viable offspring. Divergent Evolution Occurs when isolated populations of a species evolve independently. Grizzly Bear Polar Bear Divergent evolution is responsible for polar bears. A northern population of grizzly bears became isolated from others of the species and adapted to the Arctic regions. Coevolution Interactions with other organisms effect evolution. Coevolution is responsible for mimicry one of the most fascinating topics in biological evolution. Coevolution The pronuba moth and the yucca flower Depend on one another for reproduction. Coevolution The Orchid Fly Coevolution Cactus and Galapagos Tortoise Saddleback shell Cleaner Wrasse Sabre Toothed Blennie Adaptive Radiation Many diversely related species from one common ancestor Polyploidy in Plants If plants inherit an extra chromosome from parents, they are said to be polyploidy. Often, these plants can only mate with other polyploids, or use asexual reproduction. Convergent Evolution Unrelated species display similar features. No common ancestor. How does this happen Convergent Evolution Disruptive markings make it hard for predators to single out a victim. Similar niches usually contain similar evolutionary pressures selective pressures. If ancient niches were similar to modern niches then organisms today could resemble organisms now long extinct. Similar niches found on different continents can produce organisms that are fairly similar. Modern dolphins and prehistoric ichthyeosaurs marine reptiles look very similar due to the types of niche they inhabited. Analogous structures can be caused by niches. Similar niches create similar body forms. . . . .. Note how similar niches created long necks in both sauropods and giraffes. . . . Similar foods similar niches create similar teeth in herbivores. . Similar foods similar niches create similar teeth in carnivores. Quick Quiz . What are isolating mechanisms, how do they operate . What is polyploidy What is its connection to speciation . Explain the statement Populations evolve, not individuals within a population. Origin of Species Concept Review New species can develop when populations become separated and isolated. Similar traits can develop in unrelated species occupying comparable niches. Interactions with other organisms affect evolution. Many diverse species can evolve from one ancestral species. Chapter The Origin of Life Objectives Describe the origin of the universe and probable conditions on early Earth Evaluate hypotheses about the origin of life and identify the probable characteristics of early lifeforms Distinguish between chemical and biological evolution Describe the fossil record for prokaryotes and eukaryotes. The Origin of Life Cant be observed Inferences Probably needed energy, C, H, O, N, and lots of time. The Big Bang The Expanding Universe Edwin Hubble, . The Hubble Telescope was named for him. Wavelengths of light can be measured, spread out as objects move farther away The rate of expansion is known, used to calculate the time when universe was tiny. The Big Bang billion years ago Universe was condensed into a tiny singularity An infinitely hot, dense mass. When it exploded, The Big Bang, hurled energy and mass into space. What was there before the Big Bang Early Earth . Billion years ago Meteorites and the oldest rocks from the Moon confirm this History of the Earth Era Cenozoic Mesozoic Million Years Ago First evidence of Humanlike apes Primates Flowering Plants Mammals Dinosaurs Reptiles Amphibians Land Animals Land Plants Vertebrates Eukaryotes Free O in atmosphere by prok. Prokaryotes Paleozoic Precambrian The Early Atmosphere Gasses from volcanoes N, CO, HO, H, CO, probably methane CH No O No ozone layer intense radiation, extreme temperature changes. The First Living Things Anaerobic Organisms billion years later, some photosynthetic organisms began releasing free oxygen. . Life originated on some other planet, then traveled to Earth through space. . Life originated by unknown means on Earth . Life evolved from nonliving substances through interaction with their environment. of these cannot be tested, only one can be stated as a hypothesis. Which one How did those living things come to be possible explanations Chemical Evolution Life evolved from nonliving substances Small, inorganic molecules were heated via cosmic radiation, volcanoes, radioactivity and lightning. Gasses in the atmosphere react, forming organic compounds Compounds accumulate in oceans, forming a hot soup Life evolved by chemical reactions and transformations in the organic soup Chemical Evolution The oceans became soup of organic compounds The Heterotroph Hypothesis The first living things were probably heterotrophs that fed on organic compounds in the ocean. With no competition, autotrophs would not have an advantage over heterotrophs . There had to be a supply of organic molecules, produced by nonbiological processes. . Some processes had to assemble those small molecules into polymers such as nucleic acids and proteins. . Other processes had to organize the polymers into a system that could replicate itself The Heterotroph Hypothesis or OparinHaldane hypothesis Requirements Evidence for the Heterotroph Hypothesis Stanley Millers experiment in . Early Earth conditions were simulated in an airtight apparatus. Water vapor Lightning CH, NH, HO, H After circulating for a week, new compounds were found in the water, including some amino acids. More recent experiments have produced the bases of DNA and RNA too. Other Sources of Organic Molecules Meteorites from space amino acids have been discovered Volcanic vents release gases at high temperatures Remember st requirement There had to be a supply of organic molecules, produced by nonbiological processes. The rest of the hypothesis . Some processes had to assemble those small molecules into polymers such as nucleic acids and proteins. Clay repeating crystalline structure that could attract then connect monomers . Other processes had to organize the polymers into a system that could replicate itself RNA Can form spontaneously. Can reproduce itself. Probably came before DNA Biological Evolution When did chemical evolution become biological evolution When organic molecules became living things Self reproduction, mutation that can be inherited, and natural selection life Cells Today all living things are made of cells. It is unknown when/how cell membranes developed. The first living things may have had membranes, or not. They may have been DNA, RNA, proteinswho knows Prokaryotic Fossils . Billion years old. Singlecelled prokaryotes. Suggest life was already diverse and thriving. Probably methanogens Use CO to oxidize hydrogen Fossils of Eukaryotes . Billion years old Lynn Margulis of UMass, Amherst developed the endosymbiont hypothesis Chloroplasts and mitochondria were once freeliving prokaryotes. Photosynthesis and respiration of the small cells have benefited the host cells. Mitochondria probably evolved from aerobic, heterotrophic purple bacteria. Plastids probably evolved from autotrophic cyanobacteria. Endosymbiont Hypothesis The evidence Both have their own DNA and ribosomes, which are similar to other bacteria. Also both have a double membrane their outer membranes may have evolved from vacuoles when host cells took them in. Evolution of Eukaryotes Quick Quiz . Why is it believed that methanogens might have been the first organisms . How might mitochondria and plastids have originated . What evidence supports the idea that mitochondria and plastids originated from freeliving prokaryotes Outcomes Describe how modern humans differ from other primates Evaluate the techniques used to study evolutionary relationships in humans Compare early hominids with Homo erectus and Homo sapiens Give reasons for the difference in the gene pools of modern human populations. Chapter Human Evolution What are Primates Opposable Thumbs Fingers and toes have nails, not claws Flexible shoulder and hip joints Binocular, D vision for accurate depth perception Color vision Humans vs. Other Primates Bipedal Hands are free Have a hippocampus brain region for memory and learning. Absent in most primates not chimps and gorillas More fine motor control in hands Language, well developed vocal chords Molecular Similarities Human vs. Chimpanzee Protein Hemoglobin Myoglobin Cytochrome C Serum Albumin Number of amino acids Aminoacid difference Molecular Similarities Among Primates Species compared Difference in DNA sequence Chimpanzee vs. . Bonobo Human vs. . Chimpanzee Human vs. . Gorilla Gorilla vs. . Chimpanzee Estimated time since divergence million years million years million years million years Early Hominids Lived in Africa Genera in Hominid family Homo and Australopithecus larger teeth, smaller brains. The Hominids Hominids The Humanlike Primates Comparing Skeletons Skeletal fossils clues to how organism moves, eats, behaves. Footprint fossils How organism moved, how heavy it was. Who was Lucy Comparing Skeletons Skeletal fossils clues to how organism moves, eats, behaves. Footprint fossils How organism moved, how heavy it was. Who was Lucy Australopithecus afarensis found in Ethiopia, The First Humans Hominids Hence, both in space and time, we seem to be brought somewhat near to that great fact that mystery of mysteries the first appearance of new beings on this earth. Charles Darwin