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Biology Class Notes Lesson 28 Natural Selection Objective: 3.4.2, 3.4.3 Species: A group of organisms that can interbreed to produce fertile offspring. • Organisms thrive in environments where they are best suited. • Species develop/evolve characteristics to help them survive in their environments. Speciation: The evolutionary process that produces new species. Gene Pool: All the genes or genetic variation within a population. Variation: Differences among members of a species. • If variation gives an organism an advantage in its environment, it will be more likely to survive and reproduce. Inheritable Characteristics: Variation in an organism that is inheritable (i.e. passed to offspring). Methods of Speciation Geographic Isolation • The physical separation of members of a population that results in the inability to mate. • Can be caused by bodies of water, mountains, valleys, deserts, etc. • Natural selection on each side of the barrier causes the populations to become genetically different. Reproductive Isolation • Barriers to successful breeding between population groups in the same area. • Can be caused by: incompatible behavior (mating calls that aren’t recognized), differences in mating times, or physical differences that cause individuals to choose specific, nonrandom mates. • Nonrandom mating causes genetic differences. Parapatric Isolation • Can affect two neighboring populations living in different environments next to one another. Ex: Dry vs. wet, cool vs. hot, high altitude vs. lower altitude, etc. • Natural selection favors different adaptations in each environment and the populations become genetically different. Behavioral Isolation • Results from differences in behaviors, such as choosing to migrate at different times that prevent mating. • Selection of nonrandom mates results in genetic variation Natural Selection: The nonrandom process by which biologic traits become more or less common in a population as a function of differential reproduction (i.e. organisms best suited for their environment, as a result of favorable characteristics, will survive and reproduce). • First proposed by Charles Darwin 1. Most organisms produce more offspring than can survive. 2. This results in competition for resources. 3. Some offspring will have variations that make them better at competition and better able to survive. 4. Successful organisms reproduce and pass these successful traits to their offspring. 5. Over time, these successful traits are found in more and more offspring. Adaptation • A trait that improves an organism’s chance for survival and reproduction. • Adaptations lead to favorable traits that lead to evolution… Types of Natural Selection Stabilizing Selection • Individuals with the average form of the trait have the highest fitness Directional Selection • Individuals with one extreme form of a trait that results in greater fitness over individuals with an average form of a trait. Disruptive Selection • Individuals with either extreme variation of a trait have greater fitness than individuals with the average form of the trait Sexual Selection • Females choose the males they mate with based on certain traits (e.g. brightly colored feathers, strength, intelligence, speed). • The traits communicate a male’s fitness to the females. Antibiotic Resistance Natural antibiotics and bacteria have always evolved. A form of drug resistance in which sub-populations of resistant bacteria flourish while non-resistant sub-populations are eliminated. Leads to new infections that are not treatable with conventional antibiotics. Bacteria that develop resistance to first and second line antibiotics are called Multidrug Resistant or MDR (a.k.a Superbugs). Should you take antibiotics when you are not sure about whether an illness is caused by a bacterial infection? Problem Set: Darwin and Types of Selection Problem Set: Types of Natural Selection Key Words: Evolution Species Natural selection Adaptation Gene pool Fitness Speciation Resistance Immunity Antibiotic