Presentation on theme: "WARM-UP On your warm-up paper Your lab (dot lab)"— Presentation transcript:
1 WARM-UP On your warm-up paper Your lab (dot lab) What conditions caused the average shade of the “dot” population to evolve?Your lab (dot lab)OPEN YOUR LAB BOOKS AND HAVE YOUR GRAPHS ON YOUR TABLE
2 Change in the heritable (genetic) traits of a population over time Evolution:Change in the heritable (genetic) traits of a population over timeNote: when we discuss evolution, we are talking aboutpopulations changing, not individuals
3 The main mechanism by which evolution occurs Natural selection:The main mechanism by which evolution occurs
4 4 Conditions for Natural Selection: Variation: Individuals in a population are not identical to each other.Inheritance: Traits are passed to offspring; traits have a genetic basisEnvironmental population limits: Environmental limiting factors prevent all individuals from surviving to reproduce; some die young.
5 Environmental selection: Individuals in the population with more favorable (advantageous) traits are the ones that survive to reproduce.Individuals without advantageous traits die before reproducing.These factors result in a change in the average trait of the population… Biologists call this EVOLUTION!
6 1. VARIATIONMembers of a population have traits similar to the average trait of the entire population, but they are not identical.YOUR TURN: Using height as an example,sketch a graph to represent the statement above.Mean (average) heightFirst clarify the statement, then reveal “your turn” assignment.Discuss with students what type of graph would be best- (frequency distribution)Reveal axes as a hint while students sketch a graph on their notes sheet.Finally, reveal what the completed sketch should look likeFrequencyHeight (cm)
7 2. INHERITANCE DNA determines the traits of individuals Individuals inherit DNA from their parentsThis causes the traits of the offspring to resemble the traits of the parentsDNAmRNAproteintrait
8 3. ENVIRONMENTAL POPULATION LIMITS For all species, if every individual born into a population were to reproduce, the population would grow exponentiallyPopulationMake note to students that these graphs have different axes than the other graphs we have been examining.Time
9 3. ENVIRONMENTAL POPULATION LIMITS Environmental factors (limiting factors) prevent the majority of individuals from surviving to reproducePopulationMake note to students that these graphs have different axes than the other graphs we have been examining.Time
10 4. SELECTIONIndividuals without advantageous traits die before reproducing.Individuals with advantageous traits survive to reproduce.Again, make note the labeling of the axesFrequencydie without reproducingThese individualsThese individualssurvive to reproduceCharacteristic
11 Populations change, not individuals The “average” characteristic or other measure of the population changes over generationsaverage, 1st gen.average, 2nd gen.average, 3rd gen.average, 50th gen.Frequencydie without reproducingThese individualsdie without reproducingThese individualsThese individualssurvive to reproduceCharacteristic
12 The environment is the selective force behind evolution The environment determines what characteristics are “favorable”Because the environment changes over time, the characteristic that is more favorable for a population changesTherefore, characteristics of the population change, or evolution occursQuestions for discussion
13 WARM-UP Take out your notes sheet from last class Take out your Peppered Moth HomeworkOn your warm-up paper:What role do you think mutation plays in evolution?Where does mutation fit in with the 4 factors for Natural Selection?
14 Evolution of Peppered Moths Before we learn about how mutation influences evolution, let’s discuss the evolution of peppered moths we read about last night…Dark formPeppered form
15 Explain the evolution of color in the peppered moth population. Describe what trait evolved.Describe how each of the 4 conditions for natural selection exists in the moth example:VariationInheritancePopulation limitsSelection
16 The population of peppered moths became darker in color near industrial areas. Originally, some moths were dark, some moths were peppered (light).Color is determined by genes inherited from parents.Not all moths survive to reproduce- some are eaten by birds.Pollution killed lichen and made the environment darker, so darker moths were better camouflaged and not eaten as much as peppered (light) moths.This caused the average color of the moth population to become darker
17 Explanation revised... Controversy! Remember that evolution means change in a population’s traits. Scientists agree that evidence shows evolution of the moths has occurred.Natural selection is the mechanism for the change, and recent evidence suggests that camouflage might not be the sole reason for the environmental selection.?- Sunlight absorption and heat
18 What you will learn today… How do we measure genetic variation in a population?Why is genetic variation in a population important?What are the sources of genetic variation in a population?
19 What determines a heritable trait? DNA(gene)Observed traitmRNAproteintranslationtranscriptionprotein function(enzyme activity)Therefore, if traits vary in a population, then thegenes (alleles) must vary in the population!
20 A population with variation in traits… GreyWhiteTall earsShort ears
23 How do we measure genetic variation in a population? Gene Pool- Total genetic information available in a population (all the alleles that are present).Allele Frequency- The percentage of an allele in the gene pool. Tells you whether a given allele is common or rare.
24 Why is genetic variation in a population important? A gene pool without much variation limits a species’ ability to further evolve. (Variation is one of the 4 factors required for natural selection to cause evolution)If populations do not adapt to their environment, they may become extinct.
25 Sources of genetic variation SEXUAL REPRODUCTIONMeiosis – one allele is passed on from each parent (recall that sperm and eggs are haploid cells, each containing half the necessary genetic information).Random fertilization – only one of the millions of sperm involved in mating will fertilize the egg.The randomness of sexual reproduction explains why siblings can look so different.
26 Sources of genetic variation MUTATIONMutation means a change in DNA sequence.A new DNA sequence = new allele of a gene.Many mutations produce genes that are harmful (e.g. Huntington’s disease)Some mutations produce genes that are neutral (neither helpful nor harmful)Very, very few mutations produce genes that are advantageous
27 Mutations add new alleles to the gene pool Mutations add new alleles to the gene pool. That is, they increase the variety of alleles in the population.
28 Deck of Cards AnalogyDeck is Gene Pool – It contains all possible alleles for the next generation.Drawing cards picks the alleles that are inherited by the next generation.Shuffling of the deck is sexual reproduction.Adding new cards to the deck is mutation.(Mutation is rare, but shuffling happens each time a new generation is produced)
29 Natural SelectionIndividuals with advantageous genes survive to reproduce and pass on these genes to their offspring.Individuals without advantages genes do not survive to reproduce, and these genes do not get passed on in the population.
30 Conclusion Mutation does NOT cause evolution it is only a source of variation (just one of the factors required for natural selection)Natural selection determines if the allele frequency will change within a population.Change in allele frequency = EVOLUTIONExplain the change in allele frequency in the peppered moth population.
31 WARM-UP 1. Define “theory” in your own words. 2. What is the difference between the way scientists use the word “theory” and the way we use it in regular conversation?3. How are theories made?
32 Directions Make observations about the cube Develop a hypothesis for the “rules” defining the relationships between the letters, numbers, and colors on the sides of the cube.Make specific predictions for unknown sides based on your hypothesis.When you are ready to test your hypothesis, compare your predictions with observations of the new sides provided by your teacher.Obtain new data, observe, revise hypotheses, make new testable predictions
33 WARM-UP Did you answer the question at the end of the reading?? Compare and Contrast hypothesis and theory.Take out your Theory Cube WorksheetPut your Kerosene Karl HW in a pile on your desk