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Biology 1M03 Notes for first Test.docx

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McMaster University
Jon Stone

Biology Notes for first Test Chapter 1- Biology and the Tree of Life  Biological Science was founded with the development of the cell theory and the theory of evolution by natural selection  Phylogenetic tree- a diagram used to represent evolutionary relationships among species; can be established by analyzing similarities (and differences) in traits  Cell Theory- Robert Hooke (viewed cork cells from oak bark) and Anton van Leeuwenhoek (viewed single-celled “animalcules”), were the first scientists to observe cells; states that all organisms are made of cells and all cells come from pre-existing cells (Figure 1-1)  Louis Pasteur- demonstrated that cells arise from pre-existing cells and not by spontaneous generation (straight/ swan- necked flask experiment; Figure 1-2)  Since cells come from pre-existing cells, all individuals in a population of single-celled organisms are related by a single common ancestry  A multicellular organism cells are connected by common ancestry  Darwin and Wallace- proposed that all species are related by common ancestry and characteristics of species can be modified from generation to generation  Key Terms- Evolution entails that species are related to one another and can change through time, Natural Selection is a process that explains how evolution occurs, Fitness may be conceptualised as the ability of a typical individual (within a group) to survive and produce offspring, Adaption may refer to a trait that increases the fitness of a typical individual in a particular environment.  A group of individuals of the same species living in the same area constitutes a population  Two conditions necessary for Natural Selection to occur in a population: individuals in the population vary among themselves in characteristics that are heritable and in a particular environment, certain versions of these heritable traits help individuals survive better or reproduce more than do other versions.  If certain traits increase fitness, they become more common in the population over time  Natural Selection acts on individuals, but evolutionary change affects only populations  Artificial Selection- individuals in a population are selected for a mating based on particular traits (example: Figure 1-3a)  Speciation- is a divergence process in which natural selection has caused a population of one species to diverge to form a new species. (Figure 1-4)  Taxonomic Levels- Linnaeus’ system: kingdom, phylum, class, order, family, genus, species (Figure 1-5)  5 kingdom system- Figure 1-7  Difference between Eukaryotic cells and Prokaryotic cells- membrane-bound nucleus versus no membrane-bound nucleus (respectively; Figure 1-6)  Carl Woese and rRNA- rRNA was used as a means for understanding evolutionary relationships among organisms: rRNA sequences should be very similar in closely related organisms and in a phylogenetic tree, branches that are close to one another represent species that are closely related.  Figure 1-8: Nucleotide sequences from the SSU rRNA gene- comparing the changes in sequences of the rRNA gene  Phylogenetic Tree of Life- Domain Bacteria, Domain Archaea and Domain Eukarya (rRNA found in all of these organisms and are compared to see how closely related organisms are to one another (Figure 1-9)  The 3 major groups of organisms in the Tree of Life have two groups of prokaryotes: Bacteria and Archaea and the Eukarya (not all prokaryotes share a common ancestor)  The Sexual Competition Hypothesis- that giraffes did not develop long necks because of feeding in high spots in trees, but because longer-necked males win more fights that short-necked males and that allows them to father more children  A null hypothesis- specifies what we should observe if an experimental treatment has no effect  The Directed Dispersal Hypothesis- states that the molecule capsaicin in chili peppers is an adaptation that discourages seed predation while not preventing seed dispersal (Figure 1-11)  Elements in a Well-Designed Experiment: it includes a control group to check for other factors that might influence the outcome, experimental conditions are controlled to eliminate other variables and the test must be repeated to reduce the effects of distortion due to small sample size. Chapter 24- Evolution by Natural Selection  Populations and species evolve, meaning that their characteristics change through time; evolution may be defined as changes in allele frequencies  Natural Selection occurs when individuals with certain alleles survive or produce more offspring, in a population  Evolution by natural selection is not progressive and it doesn’t change the characteristics of the individuals that are selected  Animals do not do things for the good of the species and not all traits are adaptive  In the theory of evolution through natural selection, Charles Darwin and Alfred Russel Wallace made the claim that evolution has occurred  Fossils- are the first evidence of organisms that lived in the past; described in the fossil record (fossils appearing at different times in the geological time scale); most fossils are found in sedimentary rock; provide evidence for extinct species  Earliest signs of life are found in rocks from about 3.4 billion years ago  Transitional Forms- fossils that have been discovered with traits that are intermediate between earlier and later species (between other groups of fossils; example is during the evolution of whales, Figure 24-4)  Vestigial Traits- is a reduced or incompletely developed structure in an organism that has no function or reduced function but is similar to functioning organs or structures in closely related species (examples in humans are the tail bone and goose bumps).  Phylogeny- a family tree of populations or species (Figure 24-6)  Homology- a similarity that exists in species descended from a common ancestor; 3 levels: genetic, developmental and structural  Genetic Homology- is a similarity in the DNA sequences of different species  Process of Natural Selection in 4 steps: 1. Individuals that make up a population vary in their traits (variation), 2. Some of these trait differences are heritable (heritability), 3. In each generation many more offspring are produced than can survive (competition), 4. Individuals with certain heritable traits are more likely to survive and reproduce (skewness; uneven distribution).  Evidence for Evolution (Figure 24-1)  Evolution may be defined more specifically as a change in allele frequencies in a population over time (Example in a population of moths: Figure 24-1)  Structural Homology- refers to similarities in adult morphologies (example: bones found in the limbs in vertebrates; Figure 24-9)  Developmental Homology- is a similarity in embryonic traits; example is the gill pouches found during embryonic development in chicks, humans and house cats (Figure 24-8).  Good example of Natural Selection- a mutation in Mycobacterium tuberculosis (causes tuberculosis) that allows the bacteria to develop drug resistance, not being killed by the antibiotics and eventually killing the host. Natural Selection acts on an individual (the human) and populations evolve (the bacteria), as allele frequencies change.  A change in a trait of a small population is considered to be the bottle neck effect (Figure 24-12)  Evolution by Natural Selection is not goal directed; it is simply favoring individuals that happen to be better adapted to the environment at the time. Adaptions do NOT occur because organisms want or need them.  Evolution produces a Tree of Life  Animals do NOT do things for the good of the species, individuals with “self-sacrificing” alleles die and do not reproduce offspring. However, individuals with “selfish” alleles do survive and produce offspring, as well as increase in frequency. (Figure 24-16)  Genetic Constraints- selection is not able to optimize all aspects of a trait due to certain genetic constraints.  Genetic Correlation- occurs when selection favoring alleles for one trait causes a correlated but suboptimal change in an allele for another trait.  Lack of genetic variation can also constrain evolution, because natural selection can work only on existing variation in a population.  Fitness Trade-Off: is a compromise between traits, in terms of how those traits are adapted for the environment  When traits evolve from previously existing traits, adaptions are constrained by history. iClicker Questions 1. Darwin described evolution with the phrase: “descent with modification.” What did he mean? Closely related species are similar at the genetic, development and structural levels. Populations living today are related (genetically) to populations that lived in the past, but they are not identical. 2. What will happen to the size and shape of the beaks in medium ground finches, in the future? It depends on changes in the environment. 3. Which of the following statements is correct? A. Mycobacterium tuberculosis populations around the world will get more and more drug resistant over time. B. Evolution by natural selection is not progressive. It is random. C. The largest, strongest, and most dominant individuals in a population produce the most offspring. D. In 1977, individual finches adapted to drought conditions and passed those traits on to their offspring. E. None of the above Chapter 25- Evolutionary Processes  The Hardy-Weinberg Principle acts as a model for generating predictions consistent with a null hypothesis when researchers want to test whether one among 5 factors is affecting a particular gene.  Four factors affect allele frequencies directly and each has different consequences.  Natural Selection produces Adaption  Genetic Drift produces stochastic (statistically unpredictable) fluctuations in allele frequencies  Gene Flow (migration) equalizes allele frequencies between populations.  Mutation introduces new alleles  Inbreeding (through “selfing”) changes genotype frequencies but does not change allele frequencies.  Sexual Selection leads to the evolution of traits that help individuals attract mates (usually affects more strongly the gender that invests less in offspring and benefits more from being promiscuous than traits of the gender that invests more in offspring and benefits more from being choosy).  THE 4 FACTORS THAT CHANGE ALLELE FREQUENCIES: Natural Selection, Genetic Drift, Gene Flow and Mutation.  Using the Hardy-Weinberg, scientists imagined that all the gametes produced in each generation go into a a single group called a gene pool (Figure 25-1)  Their calculations predict the genotypes of the offspring that the population would produce, as well as the frequency of each genotype.  The frequency of A i1 represented by p and the frequency of A is 2epresented by q. Since there are only two alleles, p + q = 1  Three genotypes are possible: A A1, 1 A1a2d A A (2i2ure 25-2) 2 2  To represent 100% of the population: p + 2pq + q = 1 This is the Hardy-Weinberg Equation  The Hardy-Weinberg principle holds true when the following five assumptions/conditions are met with respect to the gene in question: no natural selection, no genetic drift, no gene flow, no mutation and no biased mating.  H-W principle serves as a model for generating predictions consistent with a hypothesis for determining whether a factor is acting ultimately on a particular gene in a population.  Examples in the H-W principle in Table 25.1 and Table 25.2; Read pages 530-532  Natural Selection occurs in a wide variety of patterns: Heterozygote advantage- where heterozygote individuals have higher fitness than homozygous individuals do. This pattern maintains genetic variation in a population.  Genetic Variation- refers to the number and relative frequency of alleles that are present in a particular population.  Maintaining Genetic Variation is important because lack of variation can make populations less able to respond successfully to changes in the environment.  Directional Selection- is a pattern of natural selection that increases the frequency of one allele; this type of selection reduces a population’s genetic diversity over time.  If directional selection continues over time, the favored alleles eventually reach a frequency of 1.0 (or 100%). These alleles that reach a frequency of 1.0 are said to be fixed, alleles that are no longer found in the population are said to be lost.  Stabilizing Selection (pattern of natural selection)- occurs when individuals with intermediate traits reproduce more than others, thereby maintaining intermediate phenotypes in a population.  Distributive Selection (pattern of natural selection)- occurs when intermediate phenotypes are selected against and extreme phenotypes are favored.  Distributive Selection maintains genetic variation but does not change the mean value of a trait and can cause speciation if individuals with one extreme of a trait start mating preferentially with individuals that have the same trait.  Genetic Drift- is any change in allele frequencies in a population due to chance (sampling error), it causes allele frequencies to drift up and down over time, is unbiased with respect to fitness (frequencies are not adaptive) and over time genetic drift can lead to fixation of alleles.  Genetic Drift is more pronounced in small populations than in large ones, however, given enough time genetic drift can be an important factor even in large populations.  Genetic Drift has been found to decrease genetic variation within populations and increase genetic differences between populations.  Genetic Drift can be caused by any event or process that involves sampling error; two examples are the founder effect and bottlenecks.  Founder Effect- occurs when a group migrates to a new area and starts a new population; if the group is small then its allele frequencies probably differ from those of the source population; it is especially common in the colonization of isolated habitats such as islands, mountains, caves and ponds.  Population Bottleneck- a sudden decrease in population size; commonly caused by disease and natural catastrophes. They lead to genetic bottlenecks (which is a sudden reduction in the number of alleles in a population).  Gene Flow (migration)- the movement of alleles from one population to another, occurs whenever individuals leave one population, join another, and breed. (Figure 25-8)  Mutation restores genetic diversity by creating new alleles; is unbiased cause changes in functioning genes, most of them result in deleterious (eventually removed by selection), alleles that lower fitness.  Rarely does mutation produce a beneficial allele that should increase in frequency in a population due to natural selection.  Mutation can be a significant evolutionary factor in bacteria and archaea, which have short generation times.  Mutation is relatively slow compared to natural selection, genetic drift and gene flow.  Biased Mating- mating that may not be unbiased with respect to any particular gene in question; two mechanisms that violate the H-W assumption of unbiased mating are inbreeding and sexual selection.  Inbreeding (mating between relatives)- increases the frequency of homozygotes and reduces the frequency of heterozygotes in each generation; does not cause allele frequencies to change in the population as a whole ; it changes genotype frequencies but not allele frequencies.  Inbreeding Depression- is a decline in average fitness that takes place when homozygosity increases and heterozygosity decreases in population; can increase the rate at which natural selection removes disadvantageous recessive alleles by exposing these alleles in the homozygous phenotype.  Evolutionary Mechanisms Summary in Table 25-4  Sexual Selection occurs when individuals within a population differ in their ability to attract mates; favours individuals with heritable traits that enhance their ability to attract to obtain mates.  F
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