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• Those w/ favorable, heritable traits are more likely to survive and
• Frequency of favorable traits will increase (as will their alleles);
frequency of unfavorable traits will decrease (as will their allels). 22
22 How Does Natural Selection
Cause Allele Frequencies to Change? Alleles representing favorable traits
survive and become more common in the population (↑ frequency)
Alleles representing unfavorable traits
become less common (↓ frequency) or are removed (↓ variation) 23
23 Genetic Drift
When chance events cause unpredictable changes
in allele frequencies from one generation to the next i.e. by chance either + or – alleles may increase in the next generation
vs. Natural selection in which changes are predictable since
specific (+) phenotypes and their associated alleles are favored 24
24 What type of chance events cause Genetic Drift? e.g. Chance survival of individuals
causes random fluctuations in allele frequencies Allele that causes the
increased in frequency
due to luck not
because it is better. GD could randomly result in the complete loss of an allele GD is most influential on small populations Unlike NS which always ↑ good alleles and ↓ bad ones,
GD can ↑ either good or harmful alleles (and ↓ either too) 28
28 A Popu...
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