Presentation on theme: "WARM-UP On your warm-up paper –What conditions caused the average shade of the “dot” population to evolve? Your lab (dot lab) –OPEN YOUR LAB BOOKS AND."— Presentation transcript:
WARM-UP On your warm-up paper –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
Evolution: Change in the heritable (genetic) traits of a population over time Note: when we discuss evolution, we are talking about populations changing, not individuals
Natural selection: The main mechanism by which evolution occurs
4 Conditions for Natural Selection: 1.Variation: Individuals in a population are not identical to each other. 2.Inheritance: Traits are passed to offspring; traits have a genetic basis 3.Environmental population limits: Environmental limiting factors prevent all individuals from surviving to reproduce; some die young.
4.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!
1. VARIATION Members of a population have traits similar to the average trait of the entire population, but they are not identical. Frequency Height (cm) Mean (average) height YOUR TURN: Using height as an example, sketch a graph to represent the statement above.
2. INHERITANCE DNA determines the traits of individuals Individuals inherit DNA from their parents This causes the traits of the offspring to resemble the traits of the parents DNAmRNAprotein trait
3. ENVIRONMENTAL POPULATION LIMITS A.For all species, if every individual born into a population were to reproduce, the population would grow exponentially Time Population
B.Environmental factors (limiting factors) prevent the majority of individuals from surviving to reproduce 3. ENVIRONMENTAL POPULATION LIMITS Population Time
4. SELECTION Individuals without advantageous traits die before reproducing. Individuals with advantageous traits survive to reproduce. These individuals die without reproducing These individuals survive to reproduce Frequency Characteristic
Populations change, not individuals The “average” characteristic or other measure of the population changes over generations Frequency Characteristic average, 1 st gen. These individuals die without reproducing average, 2nd gen. These individuals die without reproducing average, 3rd gen. average, 50 th gen. These individuals survive to reproduce
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 changes Therefore, characteristics of the population change, or evolution occurs Questions for discussion
WARM-UP Take out your notes sheet from last class Take out your Peppered Moth Homework On your warm-up paper: 1.What role do you think mutation plays in evolution? 2.Where does mutation fit in with the 4 factors for Natural Selection?
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 form Peppered form
Explain the evolution of color in the peppered moth population. 1.Describe what trait evolved. 2.Describe how each of the 4 conditions for natural selection exists in the moth example: 1.Variation 2.Inheritance 3.Population limits 4.Selection
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
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
What you will learn today… 1.How do we measure genetic variation in a population? 2.Why is genetic variation in a population important? 3.What are the sources of genetic variation in a population?
What determines a heritable trait? DNA (gene) mRNAprotein Observed trait transcription translation protein function (enzyme activity) Therefore, if traits vary in a population, then the genes (alleles) must vary in the population!
A population with variation in traits… Grey White Tall ears Short ears
...is caused by variation in alleles Grey allele = G White allele = g Tall ear allele = T Short ear allele = t T t G t g T G g t G g t G g t G g t G T t g
How do we measure genetic variation in a population? Grey allele = G White allele = g Tall ear allele = T Short ear allele = t T t G t g T G g t G g t G g t G g t G T t g “Gene Pool” 8 / 16 = 50% G 8 / 16 = 50% g 4 / 16 = 25% T 12 / 16 = 75% t
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.
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.
Sources of genetic variation 1)SEXUAL REPRODUCTION A.Meiosis – one allele is passed on from each parent (recall that sperm and eggs are haploid cells, each containing half the necessary genetic information). B.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.
Sources of genetic variation 2)MUTATION Mutation 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
Mutations add new alleles to the gene pool. That is, they increase the variety of alleles in the population.
Deck of Cards Analogy Deck 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)
Natural Selection Individuals 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.
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 = EVOLUTION Explain the change in allele frequency in the peppered moth population.
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?
Directions 1.Make observations about the cube 2.Develop a hypothesis for the “rules” defining the relationships between the letters, numbers, and colors on the sides of the cube. 3.Make specific predictions for unknown sides based on your hypothesis. 4.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
WARM-UP –Did you answer the question at the end of the reading?? –Compare and Contrast hypothesis and theory. Take out your Theory Cube Worksheet Put your Kerosene Karl HW in a pile on your desk