NATURAL VS. ARTIFICIAL SELECTION
Natural Selection An individual that has a selective advantage is more likely to survive, reproduce and pass on its characteristics to its offspring Eventually, the selective advantage is likely to become a common characteristic in the population..known as natural selection
COPY Natural Selection Definition: the process by which characteristics of a population change over many generations as organisms with heritable traits survive and reproduce, passing their traits to offspring. It is situational. Selective advantages are different in different environments It can only take place where there is variation in a population Survival of the fittest
consider a population of young trees In a dense forest with low light, only trees able to survive in the shade will reproduce and pass on alleles to survive those conditions In the next generation, the abundance of these alleles will increase because more of these individuals have survived and reproduced Over time, the tree population will be able to survive shady conditions
.should there be an big increase in the light levels the trait for resisting these conditions will no longer be an advantage..but if no individuals in the population can withstand increased light levels, the population may not survive
Activity: Modelling Natural Selection A certain bear likes to eat berries. In the bear s environment, there are two kinds of berries: blueberries and raspberries. The blueberries are sweet and easy to pick. The raspberries are sour and difficult to pick because the bushes are filled with thorns. Therefore, in this environment the bear chooses blueberries over raspberries. All the berries ripen every summer. In this activity, you will be the bear and model natural selection
Materials: 80 blue counters 10 red counters Bag or cup Graph paper
Procedure: 1. Work in groups of four. Create the following data table to record your data: Season 1 Season 2 Season 3 Season 4 Total number of berries Number of blueberries Number of raspberries
2. Each group will be given a bag of 20 berries 3. Each bear in your group eats four berries each year. To eat four berries, remove four counters (remember they prefer blueberries). If you do not have four blueberries in your bag, then eat whatever blueberries you do have plus one to three raspberries. 4. A season passes. Each berry left in your bag produces four new berries of the same colour, for a total of 20 for the next season. Replenish your supply of berries from Ms. Keller and record under season 1 in your table. 5. Repeat steps 3 and 4 for three more seasons of berries 6. Graph your results.
Questions 1. What happened to each population of berries? Explain. 2. Is this an accurate model of natural selection? Explain.
Artificial Selection Natural selection describes changes to a population caused by environmental pressures and selective advantages Artificial selection describes changes to a population caused by deliberate, selective breeding by humans Traits that humans select as desirable.aren t necessarily traits that would increase a population s fitness to survive in the wild
copy Artificial Selection Definition: selective pressure exerted by humans on populations in order to improve or modify particular desirable traits
Cats All domestic cats are the same species, so they can interbreed and produce viable offspring..but over generations breeders can change how a particular cat breed looks Siamese Egyptian Sphynx Cat Persian cat
Food crops The food crops we depend on for more of our diet rice, corn, wheat, and vegetables are the result of selective breeding Example, the wild mustard plant has been modified by selective breeding to create vegetables like broccoli, brussel sprouts and cauliflower Starting over 4000 years ago in Europe and Asia where the wild mustard plant is a native species..since they are all members of the same species, they can interbreed and form viable offspring..have you seen a brocciflower at the grocery store?
.but it doesn t always work We can breed food crops to: increase nutritional yield be drought-resistant be pest-resistant But we can t breed them to: Grow too quickly as they may not be able to tolerate poor soil conditions plants still need enough variation that they can tolerate environmental changes
Consequences of Artificial Selection English bulldogs are bred for different traits like their flat faces this trait results in severe respiratory problems German shepherds and other large dog breeds are prone to hip dysplasia and arthritis Plants that are selectively bred lack genetic diversity..but if organisms of a species are so similar, a new disease can affect an entire population
Preventative Measures To combat such disasters, gene banks have been established Gene banks contain populations of early ancestors of modern plants These specimens have been collected from the wild and from prehistoric archaeological sites Their genetic diversity can be introduced into modern plants if need arises