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GENETIC VARIATION The raw material of biological evolution Populations of organisms vary in heritable characteristics. Since the mechanisms of biological evolution act upon this variation, without it, there would be/would have been no biological evolution, and life on earth would be quite different. A simple inventory of traits of an easily obtained group of organisms (or humans) can introduce students to this concept. Materials • Representatives of a population of organisms; for example, snails, coleus, other insects or plants; several per group • Measuring tools – rulers, tape measures, scales, etc. • Magnifying glasses • Paper/pencils for recording data • Optional, and for snails only: Materials to test behaviors, such as water bottles for spraying, different foods to test preferences, stop watches to test speed of locomotion, etc. To Do and Notice The following example is for conducting the experiment with snails, but can easily be modified to any population of organisms Introduce the snails to a contained area and observe them. Do they all appear identical? How do they differ? Have a discussion of these differences with the entire class. As a class, choose at least four different anatomical or behavioral traits, and devise a way to measure or assess the variation of each trait between individuals. Record your answers. Some possible traits may be: • • • • • • • Length of foot Length of antennae when extended Color or pattern of shell Food preference “Fear” or “curiosity” Speed of retreat Height of shell Combine all the data of the class, and look for patterns. Of the four traits, are any variants more predominant in the population? Can you think of how some trait variants could be advantageous to an individual? What’s Going On? Should environmental conditions change (anything from climate to food type and availability) natural selection will favor those individuals whose genetic variations endowed them with a phenotype that allows them to survive and reproduce thereby passing on this genetically inherited trait. Over time, the genes for this trait (alleles) will become more predominant in the population as other less “fit” individuals die off and no Karen E. Kalumuck Exploratorium Teacher Institute Copyright 2006 DRAFT longer pass their genes to succeeding generations. With the passage of much time and perhaps with other mechanisms in play, a new species (or new species) may emerge from the original population. Without genetic variation and the associated phenotypic variants, should conditions change, (and conditions are always changing) a population would have no individuals who could survive and pass along their genes to succeeding generations. The population would become extinct. Karen E. Kalumuck Exploratorium Teacher Institute Copyright 2006 DRAFT