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1.A.2. Natural Selection Acts On Phenotype Natural selection acts on phenotypic variations in populations. Environments change and act as selective mechanism on populations. The environment does not directly cause changes in DNA, but acts upon phenotypes that occur through random changes in DNA Flowering time in relation to global climate change Crop production is sensitive to climate change; temperature has a large impact on the rate of plant development. Warmer temperatures will mean reduced crop yields. Peppered moth The light phenotype was favored before the Industrial Revolution. The color blended with the tree bark. After the Industrial Revolution, mostly dark colored moths were seen. They had an advantage on dark tree bark. Changes in genetic information may be silent (with no observable phenotypic effects) or result in a new phenotype. Some phenotypic variations significantly increase or decrease fitness of the organism and the population. Sickle cell anemia and Heterozygote Advantage DDT resistance in insects Humans impact variation in other species. Artificial selection Loss of genetic diversity within a crop species Overuse of antibiotics leading to increase in antibiotic resistant bacteria. Biggest problem: overuse and improper use of antibiotics, especially in livestock. Directional Selection is most common when an environment changes. One phenotype favored over another. the peppered moth Stabilizing selection maintains the status quo by favoring the mean phenotype. human birth weight Distruptive selection occurs when the extreme phenotypes are favored. May lead to speciation. Wood Frog and Leopard Frog Wood Frog Breeds in early April Leopard Frog Breeds in mid-April geographic variation – difference in variation between population subgroups in different areas A cline is a graded change in a trait along a geographic axis.