How Natural Selection CausesEvolution Key factor= environment The environment “selects” which organisms will survive.
Giraffes Variation is the raw material for natural selection. Living things face a constant struggle for existence. Only some individuals survive and reproduce. Natural selection results in genetic change Species adapt to their environment.
Kettlewell & Peppered Moths Step 1 Adaptation- an inherited characteristic that increases and organisms ability to survive and reproduce in its specific environment. knew- coloration is an inherited trait. Raised moths in lab Marked and released. Set traps to capture live moths
Kettlewell & Peppered Moths Found that 2/3 of the recaptured moths were dark (released in a polluted area) Moths that matched the trees were more likely to survive. Step 2 Using the same procedure Kettlewell released moths in an unpolluted forest. 2/3 of the recaptured moths were white. Moths matched the color of the trees.
Kettlewell & Peppered Moths Step 3 Kettlewell set up hidden cameras in the forest to record the capture of moths by birds. Results: birds are more likely to capture moths that do not match the color of the tree trunk.
Sickle Cell Anemia Homozygous recessive individuals die at an early age. Heterozygous individuals will live a normal life span. Central Africa 1:500 has the sickle cell trait Advantage of having a sickle cell allele– are not likely to contract malaria Person more likely to die of malaria than sickle cell.
Sickle Cell Anemia Balancing selection- two opposite forces affect the allele in a population. Sickle cell allele lethal=decrease Sickle cell allele protects against malaria = increase
Sickle Cell Anemia cont Balancing selection- – Situation in which natural selection for an allele is balanced by selection against it, and remains at the same frequency. • Sickle cell causes anemia • Sickle cells prevents malaria Directional Selection- – Situation in which selection for or against an allele in a population is unopposed • Sickle cell is less likely to occur in the US because it has no advantage.
Seaside Sparrows There are many different types of seaside sparrows. They have adapted to better fit into their environment. The are not different enough to be considered their own species but they have taken the first step. Divergence- an accumulation of differences between species or populations
Selective Breeding aka ArtificialSelection Choosing an organism with a desirable trait and breeding it with another organism with that same trait. Goal to produce offspring with that trait. Example:
Extinct vs. Endangered Extinct- the population of a species drops to zero. Endangered- the population is so small reproduction may be difficult. Gene pool is decreased.
Geographical Isolation Mating does not occur because of a separation of egg and sperm. Caused by physical barriers – Rivers, mountains, or other bodies of water. Createsa subspecies. If both species can still interbreed they are the same species.
Speciation The evolution of a new species. Occurs when a population of interbreeding individuals is split into separate populations. Over time these populations become a new species. (can’t interbreed)