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Chapter 21 Genetic Drift and Gene Flow

© 2014 Pearson Education, Inc.  Three major factors alter allele frequencies and bring about most evolutionary change  Natural selection  Genetic drift  Gene flow Concept 21.3: Natural selection, genetic drift, and gene flow can alter allele frequencies in a population

© 2014 Pearson Education, Inc. CWCWCWCW CRCRCRCR CRCWCRCW CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCWCRCW CRCWCRCW CRCWCRCW p (frequency of C R )  0.7 q (frequency of C W )  0.3 Generation 1 CWCWCWCW CRCRCRCR CRCWCRCW CRCRCRCR CRCRCRCR CRCWCRCW CRCWCRCW CRCWCRCW CWCWCWCW CWCWCWCW 5 plants leave offspring p  0.5 q  0.5 Generation 2 CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR 2 plants leave offspring p  1.0 q  0.0 Generation 3 Genetic Drift

© 2014 Pearson Education, Inc. The Founder Effect

© 2014 Pearson Education, Inc. Original population Bottlenecking event Surviving population (a) By chance, blue marbles are overrepresented in the surviving population. The Bottleneck Effect

© 2014 Pearson Education, Inc. Gene Flow  Gene flow consists of the movement of alleles among populations.  Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen).  Gene flow tends to reduce genetic variation among populations over time.

© 2014 Pearson Education, Inc. Central population Vlieland, the Netherlands Eastern population NORTH SEA 2 km Gene flow can decrease the fitness of a population. Parus major

© 2014 Pearson Education, Inc. Gene flow can increase the fitness of a population.