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The origins of life
The Case of The Peppered Moth (Biston betularia)
Melanin is a black pigment protein
19th century entomologists noticed that the melanic form of the moth was found in larger numbers in and around industrial regions and regions of dense human population.
(The first melanic form was thought to have been caught in Manchester in 1849)
Breed moths of different varieties to establish whether the colour was genetically controlled.
The moth colour is inherited.
(It is controlled be a polyallelic gene where the alleles for black colour are progressively more dominant to the allele for peppered colour.)
Melanism is genetic in origin and not caused by the environment.
What caused the melanic form to increase in industrial regions?
Transfer moths of both varieties to clean and polluted areas. Record the rates of predation on each variety.
Natural selection was operating through the predators, changing the proportions of the two varieties in the two areas.
Since the 1950s air pollution caused by burning coal has been controlled more effectively. the trend in industrial areas been seen to reverse the moth populations. Less melanic forms are found and more peppered forms appear.
NB Because the melanic form is caused by a dominant allele it will appear and disappear quite rapidly form the population if conditions of natural selection change.
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