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A-Level Biology OCR A

Selected Directional Selection Extreme Phenotypes Positively Moths Define

Directional selection occurs when environmental changes make the average phenotype less advantageous, favoring less common, more extreme phenotypes and shifting allele frequency towards extremes, exemplified by peppered moth coloration.

La sélection directionnelle se produit lorsqu'un changement environnemental rend le phénotype moyen moins avantageux, favorisant les phénotypes plus extrêmes et déplaçant la fréquence allélique vers ces extrêmes, comme pour la couleur des papillons phalènes.

Front Define the term directional selection and describe the consequences of it for a population. + example
Back Directional selection - when there is a change in environment & the normal/average phenotype is no longer the most advantageous
  • Organisms which are less common and have more extreme phenotypes are positively selected - allele frequency shifts towards extreme phenotypes
  • E.g. color of peppered moths - during industrial evolution, smoke killed lichens & made tree bark black so the few darker moths were positively selected and the majority (light colored) were selected against

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