TMJC Biological Evolution Notes

Page 1 of 63 Tampines Meridian Junior College JC2 H2/9744 Biology 2024 Core Idea 4A | 4B 13. Biological Evolution SYLLABUS OVERVIEW No. Overarching Idea Topics 1 Core Idea 1 The Cell and Biomolecules of Life Cell – The Basic Unit of Life 2 Biomolecules of Life and Cellular Transport 3 Core Idea 2 Genetics and Inheritance Genetics and Inheritance (I) – The Cell Cycle 4 Genetics and Inheritance (II) – DNA Replication and Gene Expression 5 Genetics and Inheritance (III) – DNA Mutations and their Consequences 6 Genetics and Inheritance (IV) – Organisation of Genome & Control of Gene Expression in Eukaryotes [Includes Core Idea 1D: Stem Cells] 7 Genetics and Inheritance (V) – Molecular Techniques in DNA Analysis 8 Genetics and Inheritance (VI) – Organisation and Inheritance of Viral Genomes 9 Genetics and Inheritance (VII) – Organisation of Genome & Control of Gene Expression in Prokaryotes 10 Core Idea 3 Energy and Equilibrium Transformation of Energy – Photosynthesis and Cellular Respiration 11 Core Idea 2 Genetics and Inheritance Genetics and Inheritance (VIII) - Inheritance 12 Core Idea 3 Energy and Equilibrium Communication and Equilibrium in Multicellular Organisms 13 Core Idea 4 Biological Evolution Biological Evolution 14 Extension Topic A Infectious Diseases Immunity and Infectious Diseases 15 Extension Topic B Impact of Climate Change on Animals & Plants Climate Change – Causes and Impacts on Animals and Plants

Page 2 of 63 NARRATIVES Core Idea 4 – Biological Evolution – helps students make sense of biology and the biodiversity of life on earth. Three important concepts within evolutionary biology are the: 1. definition of evolution and descent with modification; 2. processes of evolutionary change, natural selection and genetic drift; and 3. patterns of evolutionary relationships (depicted as phylogenetic trees or cladograms). The following questions should help students frame their learning: • Why are there so many similarities among organisms yet so many different plants, animals and microorganisms? • Why does biodiversity matter? Natural selection is the major driving mechanism of evolution The essential features of natural selection contribute to the change in the genetic makeup of a population over time. Darwin’s theory of natural selection (and, in parallel, Wallace’s similar observations and conclusions) states that inheritable variation occurs in individuals in a population. Due to competition for resources that are often limited, individuals with more favourable variations or phenotypes are more likely to survive and produce more offspring, thus passing on the alleles that code for those traits to subsequent generations. Fitness is a measure of evolutionary success as indicated by the number of surviving offspring left to produce the next generation. It is worth noting that individual organisms do not evolve; rather, it is populations that evolve. As the environment is always changing, a diverse gene pool is important for the long -term survival of a species. Genetic variation within a population contributes to the diversity of the gene pool. Changes in genetic information may be silent (with no observable phenotypic effects) or result in a new phenotype, which can be favourable, detrimental or neutral to the organism. The interaction of the environment and the phenotype determines the fitness of the phenotype; thus, the environment does not direct the changes in DNA, but acts upon phenotypes that occur through random changes in DNA. These changes can involve alterations in DNA sequences, changes in gene combinations and/or the formation of new gene combinations. Note that there is no perfect genome for organisms. Although natural selection is usually the major mechanism for evolution, genetic change in populations can occur through other processes, including mutation, genetic drift, sexual selection and artificial selection. Inbreeding, small population size, non -random mating, absence of migration and a net lack of mutations can lead to a loss of genetic diversity. Evidence of evolution by natural selection is derived from a wide range of studies, e.g. in biochemistry, morphology, genetic information from existing and extinct organisms, geology and physical science. Phylogenetic trees serve as dynamic models that show common ancestry while geographical distribution and the fossil record provide the evolutionary link between ancestral and present-day organisms. The process of evolution explains the diversity of life Changes in the gene pools of populations can occur as a result of environmental changes (including those caused by human activities) or major natural catastrophes. A diverse gene pool is vital for the survival of species when such changes occur. Small populations are especially sensitive to these forces. Mutations in DNA and recombination during meiosis are sources of variation; new genes and combinations of alleles may confer new phenotypes. Speciation and extinction have occurred throughout Earth’s history and life continues to evolve within a changing environment, thus explaining the diversity of life. New species arise when two populations diverge from a common ancestor and become reproductively isolated. Common core biological processes e.g. metabolic pathways like photosynthesis and respiration and the universal genetic code support the idea of common ancestry. Phylogenetic trees are used to model evolutionary relationships and ‘descent with modification’.

Page 3 of 63 LEARNING OUTCOMES Core Idea 4A: Natural Selection and Adaptation Natural selection occurs only if there is both variation in the genetic information between organisms in a population and variation in the expression of that genetic information, i.e. trait variation leads to differences in performance among individuals. The traits that positively affect survival are more likely to be reproduced and thus are more common in the population. The interaction of four factors is considered in evolution: 1. The potential for a species to increase in number; 2. The genetic variation of individuals in a species due to mutation and sexual reproduction; 3. The competition for an environment’s limited supply of the resources that individuals need in order to survive and reproduce; and 4. The ensuing proliferation of the organisms able to survive and reproduce better in that environment. Adaptation results from the accumulation of favourable genetic changes through natural selection, since organisms that are anatomically, behaviourally and physiologically well -suited to a specific environment are more likely to survive and reproduce. This differential survival and reproduction of organisms in a population that have an advantageous, heritable trait leads to an increase in the proportion of individuals in future generations that have the favourable trait and to a decrease in the proportion of individuals that do not. Adaptation also means that the distribution of traits in a population can change when conditions change. Changes in the physical environment, whether naturally occurring or human induced, have thus contributed to the expansion of some species, the emergence of new distinct species as populations diverge under different conditions, and the decline (and sometimes the extinction) of some species. Species become extinct because they can no longer survive and reproduce in their altered environment. If members cannot adjust to change that is too fast or drastic, the opportunity for the evolution of the species is lost. Candidates should be able to: a) Explain why variation (as a result of mutation, meiosis and sexual reproduction) is important in natural selection. b) Explain, with examples, how environmental factors act as forces of natural selection. c) Explain the role of