Transcript Evolution
Genetic Variation When we picture penguins we imagine them all the same. Perfect little carbon copies, genetic clones of black and white, wobbly, birdlike creatures that like ice. They vary greatly, however, when you take a closer look. Genetic Variation Increases the chance that some individuals will survive. Phenotypes are all of an organisms physical characteristics. Penguins – wing size, height, roundness, feather patterns, coloring….etc The greater the variation in phenotypes, the higher the probability of survival during environmental changes. Short penguins can stay warmer more easily than taller penguins and would survive extremely cold winters. Genetic Variation In warmer weather, tall, slim penguins would be better divers and could catch more fish easily. Genetic variation is stored in a populations gene pool. A gene pool is the combined alleles of all of the individuals in a population. Each allele exists at a certain rate, or frequency. An allele frequency is a measure of how common a certain allele is in the population. Word origins Pool - comes from the old french word poule. This means chicken…but poule comes from the Latin word pullus….the young of an animal. Allele Frequency Count the number of times that an allele occurs in a population then divide that by the total number of alleles. For example. If there are 8 green frogs and 5 brown frogs in a population, the allele frequency for green is 8/13 and the allele frequency for brown is 5/13. Genetic Variation Comes from two main sources: mutation and recombination. Mutation is a random change in the DNA of a gene. Recombination occurs during meiosis primarily. When gametes are made, each parents alleles are arranged in new ways. This shuffling results in different combinations. Hybridization The crossing of two different species that share common genes. Questions Natural Selection acts on _________ Phenotypes Why does genetic variation increase the chance that some individuals in a population will survive? Genetically diverse populations display high phenotypic variation. If some individuals had a resistance to a certain disease, then that small phenotype would survive. Questions If a certain traits allele frequency is 100 percent, describe the genetic variation. There is no genetic variation. Questions What might cause mutation? Exposure to radiation, insertions, deletions, unavailable resources. http://en.wikipedia.org/wiki/Mutation Distributions Normal distribution - a type of distribution of phenotypes in which the frequency is highest near the mean value and lowest toward each extreme end. Microevolution The observable change in the allele frequencies of a population over time. Natural selection can change the distribution of a trait along one of three paths: directional, stabilizing, or disruptive selection. Directional Selection A type of selection that favors phenotypes at one extreme. This will cause a shift in the phenotypic distribution. The mean will move over to the extreme value. Use the Example of Bacteria and Resistance to Antibiotics. Stabilizing Selection The intermediate phenotype is favored and becomes the most common in a population. Gall flies lay their eggs in the shoots of a plant called goldenrod. Downy woodpeckers attack larger galls and feed on the larvae inside. The wasp lays its own eggs inside small galls. After the wasp larvae emerge from the eggs, they eat the gall fly larvae. Stabilizing Selection This means that the large and small gall formations are killed and the medium sized gall fly will survive. Note that the selection against both extremes decreases genetic diversity. Disruptive Selection Occurs when both extreme phenotypes are favored. By favoring both extremes, this is how new species are developed.