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Evolution PowerPoint II Sources of variation and the results of genetic variation. Lesson Goals. Students will be able to: Describe where the genetic variation in a species comes from. Understand the results of genetic variation. Explain how changing environmental conditions affect the rate of evolution. Predict what will happen to a species that cannot adapt to a changing environment. Sources of variation There are two possible sources of variation within a population. 1. Mutation: A mutation is the change in the base sequence of DNA. Mutations that occur in the gametes (sex cells) can be passed on to the offspring in sexual reproducing organisms. Nearly all mutations are harmful. Beneficial mutations While the majority of mutations are not beneficial, sometimes random changes in the DNA give an individual a competitive advantage. An example of a beneficial mutation occurred in peppered moths. Lets take a look at what happened with these now famous moths. Peppered moths Before the industrial revolution, the dominant color of the peppered moth was a very light color. This allowed them to blend in with the tree trunks, which were also light colored. Pollution caused the trees to be covered with soot, darkening them and making the white moth stand out and become much more vulnerable to predation. A mutation for dark colored moths which once had a low adaptive value now had a much higher one. Genetic shuffling In sexually reproducing species, the far greater source of variation is comes from the shuffling of genes during meiosis and fertilization. Asexual reproducing species lack this source of variation in virtually all cases. Some unicellular organisms DO exchange genetic material with each other, but they do not need to in order to reproduce. This process is called conjugation. Evidence for evolution. There are several different sources of evidence for evolution. 1. 2. 3. 4. Fossil Records Homologous Structures DNA similarities Genetic changes within species Fossils Remains of animals and plants found in sedimentary rock deposits give us an indisputable record of past changes through time. This evidence attests to the fact that there has been a tremendous variety of living things. Some extinct species had traits that were transitional between major groups of organisms. Their existence confirms that species are not fixed but can evolve into other species over time. Homologous structures Many groups of species share the same types of body structures because they inherited them from a common ancestor that had them. This is the case with the vertebrates , which are the animals that have internal skeletons. The arms of humans, the forelegs of dogs and cats, the wings of birds, and the flippers of whales and seals all have the same types of bones (humerus, radius, and ulna) because they have retained these traits of their shared common ancient vertebrate ancestor. DNA All of the tens of thousands of types of proteins in living things are made of only 20 kinds of amino acids. Despite the great diversity of life on our planet, the simple language of the DNA code is the same for all living things. This is evidence of the fundamental molecular unity of life. The DNA code is most similar between closely related species. Humans and Chimpanzees share over 98% of their genes. Genetic change within a species This process of natural selection resulting in evolution can be easily demonstrated over a 24 hour period in a laboratory Petri dish of bacteria living in a nutrient medium. When a lethal dose of antibiotic is added, there will be a mass dieoff. However, a few of the bacteria usually are immune and survive. The next generation is mostly immune because they have inherited immunity from the survivors. Video Isn't evolution just a theory?