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Peppered Moths: Natural Selection in Action Biston betularia – melanic and peppered forms 1) What is the Genus and species name for the Peppered Moth? ......................................................................................................................................... Go to the following website and work your way through the 4 sections in order and answer the following questions. http://peppermoths.weebly.com/ 2) What is the natural habitat for Biston betularia? ......................................................................................................................................... ......................................................................................................................................... 3) What are the names of the coloured forms and how do they differ? ......................................................................................................................................... ......................................................................................................................................... 4) How could you test whether the different colouring is due to genetic or environmental causes? [Hint: think back to Mendel’s experiments with his peas.] ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 5) What is a mutation? ......................................................................................................................................... ......................................................................................................................................... 6th form | peppered Moths Natural Selection | 6) The coloured forms are due to the presence of the pigment melanin in the cells of the wings. Melanin is a protein encoded by a gene. Do mutations in the melanin gene arise because pollution levels increased? ......................................................................................................................................... 7) If natural selection was the reason for the change in the frequency of the two forms of Biston betularia, what predictions could you make? ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 8) Describe the experiments that Kettlewell carried out. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... 9) What was the main selection pressure the moths faced in their daily struggle for survival. ......................................................................................................................................... ......................................................................................................................................... 10) Put the following statements in the correct order: 1. The frequency of the allele for darker wings will increase in the population and the allele for paler wings will decrease 2. Wings that have a darker colour are better camouflaged against sooty trees 3. Better camouflaged moths have a greater probability of surviving and reproducing 4. There is a finite amount of resources available to moths that limits their population size 5. Moths produce many offspring 6. Wing colour is genetically controlled and is heritable 7. There is variation in the population of moths for wing colour 8. Thus darker coloured moths will survive to produce more offspring (they have a selective advantage) 6th form | peppered Moths Natural Selection | 11) The melanin gene has two alleles, M which produces the melanic form and m which produces the peppered form. Melanic is dominant to peppered. (a) What would be the possible genotypes of the melanic forms? ......................................................................................................................................... (b) What would be the genotype of a peppered form? ......................................................................................................................................... 12) [*extension material for mathematicians] Let the frequencies of the two alleles in a population be equal (frequency of M = 0.5, frequency of m = 0.5). (a) What is the probability that a randomly chosen moth would have the melanic form or the peppered form? ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... (b) Now imagine that the homozygous recessive form has only an 80% chance of survival compared with either the heterozygote or the homozygous dominant genotypes. We can use the term selective coefficient (s) to express this. In this case s=0.2. If we assume that the moths mate randomly amongst themselves then we would normally expect the frequency of the two alleles to stay the same in the next generation (0.5). However, with natural selection acting against the recessive allele this clearly won’t be the case. What would be the probability of sampling a moth that is homozygous recessive in the next generation after selection? ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... In fact to work out the exact probability we need to calculate it relative to the total frequency of all genotypes in the adult population by dividing by 0.95 (as is done in the following table): Genotype MM Mm mm 0.26 0.53 0.21 Frequency before selection Frequency after selection 6th form | peppered Moths Natural Selection |
