Chapter 20 - Chapter 20: Microevolution: Genetic Changes...

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Changes within Populations Penicillin came out around the height of WWII and it halted the mortality rate. o Fought the usually fatal infections of Staphylococcus aureus (a bacterium that enters the body through damaged skin. o First antibody that kills bacteria. Alexander Fleming - discovered penicillin. -1942 o 1945-Predicted that some bacteria could survive low doses and that the offspring of those germs would be more resistant to its effects. o 1950- more than half the strains were resistant. o Antibiotics create an environment favoring bacteria that are even slightly resistant to the drug. Surviving bacteria reproduce, and resistant microorganisms—along with the genes that confer antibiotic resistance— become more common in later generations. o Our use of antibiotics is comparable to artificial selection The evolution of antibiotic resistance in bacteria is an example of microevolution , which is a heritable change in the genetics of a population. o Microevolutionary change results from several processes, not just natural selection, and that sometimes these processes counteract each other. A population of organisms includes all the individuals of a single species that live together in the same place and time. Variation in natural population o Cerion snails look alike, but they are not identical; they have different weight, lengths, and diameters in shells. Different biochemistry, physiology, internal anatomy, and behavior. o Evolutionary biologists describe and quantify phenotypic variation Most characters exhibit quantitative variation : individuals differ in small, incremental ways. Difference in weight. If the sample is large enough, data is displayed by bar graph. Width of the curve is proportional to the variability—the amount of variation—among individuals. o Qualitative variation : exist in two or more discrete states, and intermediate forms are often absent. o Polymorphism : the existence of discrete variants of a character; many traits Human A, B, AB, and O blood groups. o Phenotypic polymorphisms are described quantitatively by calculating the percentage or frequency of each trait. Phenotypic variation can have genetic and environmental causes. o
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Chapter 20 - Chapter 20: Microevolution: Genetic Changes...

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