Warm-Up: 5 minutes 1.What is the difference between convergent and divergent evolution? 2.There are 3 types of selection (stabilizing, directional, disruptive). Which type of selection describes the Natural Selection lab we did with the beans? Explain. (have to think about which bean was surviving the most)

Warm-Up: 3 rd and 6 th period Get out your graphs from yesterday. Read through each scenario and graph the points. 10 minutes

Stabilizing Selection This type of natural selection favors average individuals. In this way, variation in a population is reduced. Evolution does not occur. Selection against both extremes keep curve narrow and in same place. Stabilizing Selection High mortality, low fitness Low mortality, high fitness

Directional Selection The woodpeckers with the longer beaks are more fit for this environment, so there are more of them then ones with shorter beaks. Selection for longer beaks

Directional Selection By favoring either of the extreme forms of a trait, directional selection can lead the one population to evolve into a new species.

Disruptive Selection In this type, both extreme forms of a trait are favored. In some cases, there may be no intermediate forms, which can lead to the evolution of two new species. (Speciation occurs)

Look at the two colored handouts. Compare mimicry and camouflage on the handout provided. Answer the remaining questions.

Other Evolutionary Mechanisms (Besides Natural Selection)

Mutations Harmful mutations decrease fitness Helpful mutations increase fitness

Quick Write Explain the connection between natural selection and the mutated alleles that cause sickle cell anemia using the following terms: Helpful mutation, harmful mutation, allele, frequency, population. (sickle cell anemia is when a mutation causes the blood cells to be stretched out and oddly shaped, this can cause more blockages)

Recombination Crossing over between two homologous chromosomes “mixes up” allele possibilities Increases variation among siblings

Think About It: What role does recombination play in the variation within a species? Why? Why is “Recombination” a good name for this mechanism?

Gene Flow Immigration or introduction of alleles into the population Can change the allele frequency in future populations

#2 Answer the following questions. A species of mouse contains both white and brown variations. A population of mice living in a grassy field behind a neighborhood consists of all brown mice. A white mouse of the same species wanders into the population. What happens to the gene pool of this population? What happens to the variation of this population? What do you think future generations will look like in this mouse population? Why? Why is “gene flow” a suitable name for this evolutionary mechanism?

Genetic Drift Occurs by chance with smaller populations Some variations disappear, leaving more of one variation. Over time, that variation takes over the population. (REMEMBER THAT POPULATIONS CHANGE, NOT INDIVIDUALS)

Quick Write A population of solid perch and striped perch live in a small pond. Girls in the neighborhood that fish in that pond like to keep the striped ones, but always throw the solid ones back. Draw a picture that illustrates this scenario at three different phases. Both populations living in the pond What’s in the pond after 1 year1 of taking the striped 5 years later (after genetic drift is complete) Turn to a partner and explain your pictures. Why is “Genetic Drift” a fitting name for this mechanism?

Sorting Activity Sort the cards into the 4 categories on the answer sheet given you. On the back, summarize why you categorized them. Use specific supporting evidence from the examples given you.

Sorting Activity Answers

Mutations

Recombination

Genetic Drift

Gene Flow

Summary On your answer sheet, justify why you grouped the pictures into each category. Then, explain the impact each mechanism has on the population.

Closure Checking for understanding