19.2 – Other evolutionary mechanisms
Learning objectives
• Know the non-adaptive evolutionary
mechanisms and examples
• Understand why genetic drift is more
prevalent in small populations
• Be able to analyze data and determine if a
population is evolving, and what the
mechanism is
Natural Selection leads to Adaptations
• Adaptation = a feature that has become common in a
population by natural selection, because it provides
some improved function, leading to increased fitness!
• Examples :
– a behavior or anatomical feature that allows escaping
predators,
– a protein or other compound with special
physical/chemical properties,
– an anatomical feature that allows an organism to access
resources, etc.
Non-adaptive evolutionary
mechanisms
•
•
•
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Migration (gene flow)
Mutation
Genetic drift
Non-random mating
 These mechanisms cause allele frequencies
to change, but do not lead to adaptation!
Migration is the movement of individuals
from one population to another
• If these individuals are reproducing, this leads
to gene flow
• Examples
• Consequence – populations become more
similar
Mutation is rare, but is the only mechanism
that increases genetic variation
A change in the frequency of an allele
due to the random effects of small
population size is genetic drift
• Bottleneck – an extreme example where the
population falls to a few individuals
• Founder effect/event - when a few
individuals leave a population to start their
own
founder effects
Discuss in your groups:
Why is population size important
when it comes to genetic drift?
Population size and genetic drift
Non-random mating
Inbreeding depression – reduction in fitness caused by
homozygosity of deleterious recessive mutations
Hemophilia in the British Royal family