Wednesday, September 19, 2007

evolution of populations

Hey everyone in period 8&9 AP Biology. Todays lesson was on the Evolution of populations which is covered throughout chapter 21. Today we Learned that natural selection affects populations and changes them over time, and we went into detail on how researchers know populations are changing and what causing the change. A main point of this lesson was that Individuals are selected, populations evolve Natural selection acts on individuals. Individual organisms can not evolve they are selected or not selected to survive and reproduce. Many species have adaptations to specific enviorments to prevent predation, such as pocket mice in desert lava flows, their color helps them blend in with the land to prevent themselves from being easily spotted by a predator.
There must be differences and Variation within a population for evolution to occur. Variation is the raw material for natural selection. Variation can be seen from the size of horses to the color of shells and in many other ways. The organisms with the best survival and reproductive success also know as fitness are those that pass on their traits to future generations. Sexual reproduction is successful because it makes the offspring different from the parents and hopefully passes on the traits of good fitness.
A common question would be What is a selecting force? or even, What force is acting on populations to cause a change? Well the answer can be found as one of the 5 agents of evolutionary change. These agents are Mutation, Gene flow, Non-random mating, Genetic drift, and selection. Mutations create variation. They are a change in DNA which in turn changes traits, which can be phenotypes, which is a form of variation natural selection can act upon. Gene flow is the movement of individual and alleles in and out of a population, basically through migration. Populations intermix rahter then staying isolated which affects their variation, and reduces differences between populations. This is seen in the world today with many new faces in America from countries all over the world and they are reproducing with people of other cultures to create a blending of traits. Non-random mating is mainly sexual selection which in many organisms is females choice, and not everyone has an equal chance to have offspring. Genetic drift is based on chance events. This includes the founder effect in which a small group of a population is seperated, like the finches and evolve form the genetic variation they have, making a rare allele become common. Genetic drift also includes the bottleneck which is a random event usually a disaster, that constricts a populations kills off a large percent of a population leaving a small percentage left to expand. There are many conservation issues today trying to increase variation among populations as much as possible.

and tomorrows sherpa is Mia.

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