Types of Selection (AQA A-Level Biology): Flashcards
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Stabilising selection effect
Stabilising selection effect
Maintains average phenotype by eliminating extremes
Directional selection effect
Directional selection effect
Shifts population mean toward one extreme
Phenotypes favoured by disruptive selection
Phenotypes favoured by disruptive selection
Both extremes over intermediate forms
When stabilising selection occurs
When stabilising selection occurs
When environmental conditions remain constant
Directional selection trigger
Directional selection trigger
Environmental change
Disruptive selection: frequency & importance
Disruptive selection: frequency & importance
Least common but key for speciation
Optimum human birth weight
Optimum human birth weight
Approximately 3.2kg
Peppered moth % before Industrial Revolution
Peppered moth % before Industrial Revolution
~99% light form
Peppered moth % melanic form, 1895 Manchester
Peppered moth % melanic form, 1895 Manchester
~98% melanic (dark) form
Cause of peppered moth colour shift
Cause of peppered moth colour shift
Pollution killed lichens, soot darkened surfaces