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It Is Likely That You Taught First-Year Biology Students About the “Peppered Moth”

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It Is Likely That You Taught First-Year Biology Students About the “Peppered Moth” 01 Microevolution Unique Gene Pools TEACHER NOTES It is likely that you taught first-year biology students about the “peppered moth”. Prior to starting this unit, assign students a task. Have Microevolution: Unique Gene Pools them go to this website http://www.techapps.net/interactives/pepperMoth 1 s.swf and work their way through the components of the animations. The site is very well done and it will serve as nice introduction as well as a good review of basic evolutionary concepts and how man and the environment impact natural selection. Charles Darwin • Charles Darwin (1809-1882) is credited with proposing that the mechanism for th process of evolution is natural selection. • Darwin spent five years on a voyage tha took him around the world with the majority of his time spent in South Ameri 2 and its neighboring islands. • Darwin published his theory with compelling evidence for evolution in his 1859 book On the Origin of Species, overcoming scientific rejection of earlier concepts of transmutation of species. 2 Charles Darwin http://en.wikipedia.org/wiki/Charles_Darwin contains FAR more information about Charles 3 He established that all species of life have descended over time from Darwin. common ancestors, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he calle natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding. Prior Knowledge Prior 3 Charles Darwin • By the 1870s the scientific community and much the general public had accepted evolution as a fa • However, many favored competing explanations and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 195 4 that a broad consensus developed in which natur selection was the basic mechanism of evolution. • In modified form, Darwin's scientific discovery i the unifying theory of the life sciences, explainin the diversity of life. 4 01 Microevolution Unique Gene Pools TEACHER NOTES Darwin’s Observations n • Populations change over time as evidenced by the fossil record. • There are always more offspring produced than the preceding generation. Darwin's example considers the "slowest breeder • Populations, if left unchecked, grow at a geometric rate rather than an arithmetic of all the animals", elephants. Also point out his 5 rate. • Darwin used an example involving elephants to illustrate the points above. math was a bit flawed since he neglected death He estimated that if elephants underwent unrestricted reproduction, that in 740-750 years there would be 19 million elephants rates AND did not assume a 50-50 split of male produced from just one original pair. what will happe vs. female offspring! Students will most likely ask you, “What’s the difference between geometric rate and arithmetic tion to predict rate?” The simple answer is arithmetic rates are linear, i.e. 2, 4, 6, 8, 10 etc. while geometric rates Darwin’s Observations are not linear but rely on a different mathematical function such as an exponential function. 6 These observations are what helped Charles or simulated popula or Darwin formulate natural selection as the mechanism for evolution. Natural selection is the “theory of evolution” . Evolution does occur. Species do change over time as the fossil record demonstrates. http://www.idlex.freeserve.co.uk/idle/evolution/s ex/elephant.html provides a nice explanation of the “math” thods to data from a real Darwin’s Elephant Problem “There is no exception to the rule that every organic being naturally increase at so high a rate that if not destroyed, the earth would soon be This site has a “calculator” that lets students set covered by the progeny of a single pair .... The Elephant is reckoned to be the slowest parameters relating to Darwin’s Elephant breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase: it will be under the Problem so they can understand just how wrong 7 mark to assume that it breeds when thirty years old, and goes on breeding till ninety years old, Darwin was. bringing forth three pairs of young in this interval; if this be so, at the end of the fifth century there would be alive fifteen million http://www.athro.com/evo/elframe.html elephants, descended from the first pair.” (Darwin, 1859 p.64) 7 [See SP 2.2; Essential knowledge 1.A.1] to apply mathematical me Darwin’s Observations • There is variation within a given species and the majority of this variation is inherit 8 This litter of kittens vary with respect to coat pattern and color. Emphasize that there is a difference between • Any variation may, to some degree, affect the ability of an organism to reproduce an contribute genes to the gene pool, thus affecting evolutionary success. heredity and mutation. • Species change over time. These changes are related to traits that are inherited or a from an alteration of the genetic code. • Some inherited traits are beneficial and contribute to survival. • Whether a trait is beneficial or not is a function of the environment in which it lives 8 LO 1.3 The student is able to the population in future. 01 Microevolution Unique Gene Pools TEACHER NOTES Adaptations and Fitness • An adaptation is a genetically controlled trait that is favored by natural selection and gives the organism a reproductive advantage ensuring the trait is passed on to its Ask students to compare these two hares and tural descendants. 9 identify the differences in their traits. The • This trait may also allow the individual students should come up with coat color, length to survive longer thus increasing the reproductive rate of that individual. [See SP 7.1; of ears, length of limbs, body shape, etc. 9 It’s one thing to “identify” traits and yet another Adaptations and Fitness to explain their importance or implication! The antelope hare lives in the desert, • and the snowshoe hare lives in the the environment. mountains. The long limbs of the antelope hare help • Explain how the differences in their dissipate body heat and keep the hare cool. The traits enhance their ability to survive in 10 their respective environments. brown coat color helps it to blend in with its • Evolutionary success or fitness refers to environment, thus be less obvious to potential the contribution of genes to the gene pool and NOT how long an organism predators. The snowshoe hare has smaller ears lives. and shorter limbs with a rounder body. This 10 helps keep the hare warmer. The white coat time to a change in color helps it to also blend in with its environment. The Effect of Environmental Change • Earth’s environment is NOT STATIC, but rather ever changing. • As a consequence, traits or adaptations that were favorable Environmental changes often cause a shift in may become unfavorable. • The peppered moth, Biston betularia is native to England selection pressures. Traits that were once and exists in two forms, one is dark and the other light with a “peppered” appearance. Birds are its main predator. beneficial to a population of organisms may 11 na of role the investigate quantitatively and qualitatively to ta • Prior to the industrial revolution, only 2% of the moths were dark. become detrimental and vice versa. • The industrial revolution produced vast amounts of sulfur dioxide and soot from the burning of coal which altered the environment. • Fifty years later 95% of the moths were dark. http://www.techapps.net/interactives/pepperMoth • Propose an explanation! 11 s.swf idence provided by da Explanation: The trees were previously light and Industrial Melanism covered in lichens, thus peppered moths had the advantage of camouflage over dark moths. (You England has since may have to point out the peppered moth near regulated the burning o connect evolutionary changes in a population over in a population over connect evolutionary changes coal and as a result, the the top of photo A.) trees are returning to th original state (A). 12 Consequently, the colo among the population o [See SP 2.2, 5.3; Essential knowledge 1.A.1] moths in Britain has The SO2 gas produced from the industrial shifted back so that the peppered moths are onc revolution killed the lichens. Furthermore, the again favored. soot produced during the burning of coal 12 collected on tree trunks changing their appearance and darkening them. As a result, the darker moth is now more camouflaged and less likely to be eaten by birds. LO 1.2 The student is able to evaluate ev in evolution. selection LO 1.5 The student is able to Essential knowledge 1.A.2] 01 Microevolution Unique Gene Pools TEACHER NOTES Evolution Defined • Evolution is defined as a change in the inherited characteristics of biological populations over successive generations. • Evolutionary processes give rise to Students need to be clear on the approaching diversity at every level of biological 13 organization, from the molecular to the definitions and distinctions AND have some macroscopic. illustrative examples they can discuss on the AP • As a result diversity is prevalent among molecules such as DNA as well as Exam. individual organisms and species of organisms. 13 Remind students that a gene is a sequence of DNA nucleotides that specify a particular polypeptide chain and that genes code for proteins. on over time on over Have students generate an example for each of Microevolution the 4 example “causes” of microevolution. [See SP 2.2, 5.3; to qualitatively and and qualitatively to Microevolution is simply a change in gene frequency Many correct answers are possible! within a population. • Evolution at this scale can be observed over short periods of tim such as from one generation to the next.
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