Biology 1202 Unit 1 Chapter 22 - A Descent with Modification: A Darwinian View of Life I. Evolution a) What is Evolution and Adaptation? 1. Change over time of the genetic composition of a population 2. Decent of modern organisms with modification from preexisting organisms i. Evolutionary Adaptation - Accumulation of inherited characteristics that enhance organisms’ ability to survive in specific environments b) Pre-Darwinian Theory of Evolution ii. Lamarck - Use and disuse: bodies of living organisms are modified through use or disuse of parts - Inheritance of acquired characteristics – these modifications are inherited by offspring - These ideas turned out to be wrong c) Evolution by Natural Selection iii. Darwin and Wallace developed the theory independently - Darwin – voyage of the Beagle to the Galapagos islands - Wallace – naturalist in Indonesia II. Natural Selection - The unequal survival and reproduction of organisms due to environmental factors, resulting in the preservation or keeping of favorable adaptations - This process “selects” what is best from what is available in the gene pool - New characteristics are not created on demand Mechanisms behind natural selection: Observations Drawing InferencesThink about the 100-m dash track and field competition. How can we change this race to reflect the process of natural selection? - Have people start at different times - Make the race more difficult - Change the track - Change the resources - Rewards/punishments for winners and losers In natural selection: some individuals have traits that allow them to survive longer than other individuals so they will leave genes for their offspring that will be added to gene pool III. Artificial Selection - Selective breeding of organisms to encourage the occurrence of desirable traits - Analogous to natural selection Concept 22.3 – Evolution is supported by an overwhelming amount of scientific evidence Examples of Natural Selection: Soapberry bug - beak size difference in different areas, use beaks to insert into balloon vine plantsWithin a few weeks of treatment with the drug 3TC, a patient’s HIV population consists almost entirely of 3TC-resistant viruses. How can this best be explained? a. HIV has the ability to change its surface proteins to resist drugs b. The patient must have become re-infected with 3TC-resistant viruses c. HIV began making drug resistant versions of reverse transcriptase in response to the drug d. A few drug resistant viruses were present at the start of treatment, and natural selection increased in their frequency Insert images from textbook a. Homologous & Analogous Structures: Homologous - Structures or other attributes in different species that resemble each other because of common ancestry Analogous - Structures that are similar in function but not in structure and developmental and evolutionary origin Homologous Structures: Mammalian Forelimbs Homologous Structures: Vertebrate Embryoso All vertebrates share similar developmental genes o Differences arise by some genes being switched on or off at varying times during development b. Homologous Structures: Biochemistry & Molecular Biology - DNA is universal genetic material - All life forms use approximately the same 20 amino acids to make proteins - All use ATP as the primary form of cellular energy - All use RNA and ribosomes to make protein c. Tree vs. Scala Naturae - Tree – modern way of organizing organisms, more accurate depiction, no higher or lower, just different lineages with common ancestry - Scala Naturae – lower organisms at base and higher organisms at top, progression to more complex organisms Homologies and “Tree Thinking” Convergent Evolution: - Similarity between two organisms, structures or molecules due to independent evolution along similar lines rather than descent from a common ancestorWhich of the following pairs of structures is least likely to represent homology? (common ancestor) a. The wings of a bat and the forelimbs of a human b. The hemoglobin of a baboon and that of a gorilla c. The legs of a bird and those of an insect d. The mitochondria of a plant and those of an animal Chapter 23: The Evolution of Populations The Smallest Unit of Evolution - One common misconception about evolution is that individual organisms evolve during their lifetime - Evolutionary processes (e.g., natural selection) acts on individuals, but populations evolve Concept 23.1: Genetic Variation makes evolution possible Mutation: - Mutations - changes in nucleotide sequence of DNAo Source of new alleles and genes - Point mutation: change in one nucleotide base in a gene - Chromosomal mutations: delete, disrupt, or rearrange many loci on a chromosome - Gene duplications: duplication of whole segments of a chromosome - Mutation rate averages 1 in every 100,000 genes per generation Sexual Recombination: - In sexually reproducing organisms, sexual recombination produces most of the variability in each generation Variation within a Population: - Discrete characters: classified on an either-or basis o Example: flower color in pea plants, number of students enrolled at LSU - Quantitative characters: vary along a continuum within a population o Example: height, weight Concept 23.2: The Hardy-Weinberg equation can be used to test whether a population is evolving Populations: - A group of individuals of the same species living in a certain defined area Hardy-Weinberg Equilibrium - H-W Equilibrium: describes a population that is not evolving (i.e., allele frequencies don’t change) – serves as a means of comparison - Five assumptions behind H-W equilibrium 1) No mutations 2) Large population size 3) No gene flow 4) No natural selection 5) Random mating Allele & Genotype Frequencies - Allele frequencies o p=frequency of allele 1; q = frequency of allele 2 o P+ Q = 1 - Genotype frequencieso p2 = frequency of homozygous dominant o q2 = frequency of homozygous recessive o 2pq = frequency of heterozygous o p2 + 2pq + q2 = 1 (H-W equation) Population Genetics & Human Health: - H-W equation can be used to estimate % of the human population carrying the allele for an inherited disease - PKU is a recessive genetic disorder o Frequency of homozygotes w/ this disorder is q2 = 0.0001 (1/10,000) o What is the frequency of the dominant & recessive
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