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Transient Polymorphism

IB Biology presentation for Option D:Evolution, focusing on transient polymorphism, using industrial melanism and the peppered moth as an example

Camila Herrera

on 18 September 2014

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Transcript of Transient Polymorphism

Biston Betularia: Peppered Moth
moths in Britain were light colored
1848 darker form seen in Manchester
soot from industrialization kills lichens on trees
dark moth appears
clean air act: lighter form reappears.
Transient Polymorphism
Transient Polymorphism
transient polymorphism The presence in a population at a particular gene locus of alternative alleles in which one is progressively replaced by another, in contrast to a balanced polymorphism where the alleles are in equilibrium with each other.

peppered moth is in fact a valid example of natural selection and adaptation.
Illustrates a polymorphic species maintaining adaptation to a changing environment.
peppered moth is nocturnal, which means it relies on its tree camouflage during the day to survive.
the soot deposits on trees from industrialization killed the lichens which helped hide the moths
the melanic form is given a selective advantage over the light colored form

Why is industrial melanism an example of transient polymorphism?

two alleles in which the darker one overpowers the lighter colored one over period of time.

Modern Days
last half of the 20th century, pollution law begin to be introduced, for example, 1956’s Clean Air Act
lichens start to grow back on trees
melanic form of the moth no longer has an advantage over the lighter one
selecting advantages are altered, light form reappears among the population.

Camila Herrera & Hee Won Park
What is Polymorphism?

Presence of 2 or more distinct forms of an allele in a population. Can be balanced polymorphism, or transient polymorphism.

Industrial Melanism
darkness—of the skin, feathers, or fur—acquired by a species
the environment is soot-darkened.
Melanization increases the probability of survival and reproduction
result of natural selection of the lighter, more conspicuous animals by predators.

Industrial Melanism
Balanced vs transient polymorphism:
Balanced Polymorphism:
can last for a long period
both alleles in balance
Transient Polymorphism:
usually of shorter duration
one allele in process of replacing the other
Both: Directional Natural Selection
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