Lecture 4 Concepts Key PDF

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Lecture 4 Concepts and Learning Objectives: 1. How did antibiotic resistance arise? What characteristics of bacteria make their evolution more rapid than many other species? By directional selection caused by new mutations. If these new mutations occur in the presence of amounts of antibiotics that kill their neighbors, they gain a competitive advantage and increase in number. Characteristics: short generation time and large population. 2. What is the difference between a discrete and a continuous trait? Give examples of each. Discrete traits can be binned in categories that are clearly distinguishable. Taught as binary but can fall into more than two categories, as long as they are clearly distinct (Albinism, handedness, ability to curl your tongue). Continuous traits are those that blend into one another (height, weight, hair color) 3. What is the difference between an obligate and a facultative trait? What does the reaction norm tell you about whether a trait is facultative or obligate? Obligate traits equal their genotype – h2 (the measure of heritability) is 1 or 100%. Nothing about the environment affects the phenotype. A completely facultative trait is determined by environment, and heritability is close to or equal to 0. The beetle horn size is facultative, because it is determined by the environment. If there is a reaction norm of phenotypes for a give genotype under varying environments (beetle horn size), that is indication the trait is facultative. 4. What about the Nemoria larval phenotype tells us it is a discrete facultative trait? Discrete, because the larvae are one or the other and not in between. Facultative, because it depends on the diet after hatching. 5. What generates genetic variation in a population? New variation arises by mutation. Combinatorial variation arises by genetic recombination during meiosis and by fertilization to bring together different material. 6. What does the same mutation causing the sort legged phenotype in different unrelated breeds tell us about the ancestral wolf-like population? The short-legged mutation was present in an ancestral population, and it was artificially selected again and again. 7. Why did the beaks of finches change so quickly in 1976-1977 but then revert? The drought in 1977 was strong selection for increasing beak size. Once the environment changed, there was no longer selection

against individuals with smaller beaks. Small beaks came back present in subsequent generations because their recessive alleles were still present in the genetic diversity (lecture 5 concept). 8. What is the difference between a heritability score (h2) of 0? 0.5? 1? 0 – no genetic contribution, entirely facultative. 0.5 – equivalent contribution of genetics and environment. 1 – absolutely genetic with no effect of the environment 9. How do directional, stabilizing, destabilizing, and frequency-dependent selection differ from one another with respect to the mean and variance of a population phenotype? Give additional examples of each. Directional – changes population mean in one direction, decreases variance Stabilizing – unchanged mean, decreased variance Destabilizing – unchanged mean (two ends still average to the middle), increases variance (by keeping the full range from extreme to extreme) Frequency dependent – this is the hardest one to understand. Frequency dependent is most often related to the likelihood of interaction with an outside force – the competition between fish with different size mouths. Handedness in humans is apparently another – left handedness has a disadvantage in general, but hand-to-hand fighting provides an advantage to lefties so long as they are a small enough portion if the population that they are more likely to encounter a righty than a lefty. Vocabulary Macroevolution Genotype Discrete Trait Obligate Trait Reaction Norm Directional Selection Destabilizing Selection

Microevolution Phenotype Continuous Trait Facultative Trait Phenotypic Plasticity Stabilizing Selection Frequency-dependent Selection...