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BIOA01 Chapter 17 notes

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Biological Sciences
Mary Olaveson

Chapter 17Microevolution Genetic Changes within Populations Microevolution smallscale genetic changes within populations often in response to shifting environmental circumstances or chance eventso Example evolution of antibiotic resistance in bacteria Population all individual of a single species that live together in the same place and timeScientists who study microevolution analyze variationthe differences between individualsin natural populations and determine how why these variations are inherited Darwin recognized importance of heritable variation within populations also realized that natural selection can change pattern of variation in a population from one generation to the nextMicroevolutionary changes results from several processes not just natural selection sometimes these processes counteract each other 171 Variation in Natural PopulationsIn some species individuals vary dramatically in appearance but most species the members of a population look pretty much alike Phenotypic variation differences in appearance or function that are passed from generation to generationo Examples variations in colour biochemistry physiology internal anatomy and behaviour 171a Evolutionary Biologists Describe and Quantify Phenotypic VariationQuantitative variation variation that is measured on a continuum such as height in human beings rather that in discrete units or categorieso Example weight everyone in biology class would see that mass varies almost continuously from lightest to heaviesto Also in toe lengthof hairs on heads Qualitative variation Variation that exists in two or more distinct states with intermediate forms often being absent o Example snow geese have either blue or white feathersPolymorphism The existence of distinct variants of a character among individuals in a population describe such traits as polymorphic polymany morphosform o Example 1 snail shells polymorphic in background colour number of stripes and colour of stripeso Example 2 biochemical polymorphism like the human A B AB and O blood groups Describe phenotypic polymorphisms quantitatively by calculating the percentage or frequency of each trait171b Phenotypic Variation Can Have Genetic and Environmental Causes Phenotypic variation may be caused by differences in the environmental factors that individuals experience or by an interaction between genetics and the environment Genetic and phenotypic variations may not be perfectly correlated Under some circumstances organisms with different genotypes exhibit the same phenotype
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