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Unformatted text preview: 48 XIII. Science & Evolution (Parasitology, BLY 459, 2009) A. Characteristics of a good scientific theory 1. TESTABLE a. Must make predictions; must be falsifiable b. Karl Popper: One cannot prove something is true, but one can prove something is false c. Methodology (1) Null hypothesis (a) What is tested/rejected (b) “Penicillin has no effect upon bacterial infections” (2) Control (a) Standard of comparison (b) Experimental treatment omitted (c) Placebo: Inactive substance (d) Placebo Effect: Response to act of being treated (3) Variables (a) Independent 1) Affects something 2) X-axis (b) Dependent 1) What is affected by the independent variable 2) Y-axis Slide: Growth of pleurocercoids in body tissues of mice and their effect on the body mass of their hosts. 2. Repeatable 3. Stable 4. Simple 5. Non-authoritarian 6. No retrofitting 7. Supported by convergence of independent evidence B. Basic concepts of evolution 1. Individuals within populations have different traits = variation a. Mutation creates new genes b. Genes of eukaryote offspring vary because of 2 events in meiosis (1) Crossing over Slide: Freeman 2 nd ed. Fig. 12-6 (2) Independent assortment Slide Freeman 2 nd ed. Fig. 12.8b 2. Genes enabling bearers to have more offspring become common in gene pool a. Less than 1% of all organisms that are born ever reproduce Slide: Biology in The Far Side Praying mantis lecturing students b. Maladaptive genes REMOVED from gene pool of population 3. Reproductively isolated groups eventually split/evolve into new species 4. Mechanisms 49 a. NATURAL SELECTION (1) Genes removed from population (2) Death before reproduction b. SEXUAL SELECTION (1) Females often choose the males (2) May lead to exaggerated traits (= bright plumage, heavy large antlers) that increase predation risks for those being chosen c. SYMBIOSIS (1) The ENDOSYMBIOSIS THEORY explains the origin of the eukaryotic cell (2) Eukaryotic organelles replicate independently of mitosis and possess DNA and membranes (3) Origin of the mitochondrion (a) Characteristics of the predatory host cell i Only capable of anaerobic fermentation ii Engulfs aerobic bacterium (b) Mutualistic relationship occurred i Prey bacterium not digested ii Prey provides host with abundant ATPs iii Host provides bacterium with carbon compounds and protection Slide: Figure from college introductory biology text showing origin of the mitochondrion as explained by the Endosymbiosis Theory (4) Origin of the chloroplast i. Ancestral eukaryotic cell engulfed a photosynthetic cyanobacterium ii. Prey provided host with sugars iii. Host provided cyanobacterium with carbon dioxide and protection iv. Explains presence of 3-4 membranes in eukaryotic chloroplasts Slide: Figure from college introductory biology text showing origin of the chloroplast (with 4 membranes) as explained by the Endosymbiosis Theory (5) Over evolutionary time, many organelle genes were transposed onto the host’s nuclear DNA Slide: Diagram illustrating competing ideas about the evolutionary history of the...
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- Spring '08
- Bacteria, Giraffe