III. A Closer Look at Natural Selection

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Presentation transcript:

III. A Closer Look at Natural Selection A. Natural selection, adaptation, and evolution B. Patterns of natural selection 1. Directional selection 2. Stabilizing selection 3. Diversifying selection C. Effects of selection on the distribution of phenotypes

Non-random mating affects the frequency of genotypes in a population, but does not change allele frequency Positive assortative mating Negative assortative mating AA aa aa aa X X All offspring heterozygous All offspring homozygous

Biston betularia - the peppered moth Dark morph on sooty tree Each morph on the “wrong” tree Grey moth on lichen

Industrial Melanism in the peppered moth Released in rural woodland grey melanic # released 496 473 # recaptured 62 30 % recaptured 12.5 6.3 Released in industrial region # released 137 447 # recaptured 18 123 % recaptured 13.1 27.5

Fig. 23. 12