Download Natural Selection and Adaptation - Fort Thomas Independent Schools

Gene flow is the movement of traits
between populations.
• Mechanism – Migration
• Keeps neighboring populations similar.
• Low gene flow = increased chance populations evolve into
different species.
Gene Pool
• All genes in a population
• Relative frequency = number of times an allele
occurs in a gene pool
• A normal distribution graphs as a bell-shaped curve.
– most fall in the middle
– decreases towards
each end
• Traits not undergoing
natural selection have a
normal distribution.
Normal Distribution in Humans
Most individuals lie in the middle and fewer individuals
can be found at the ends.
– Directional selection favors phenotypes (physical traits) at
one extreme.
Directional Selection in Humans
More darker skinned individuals closer to equator.
– Stabilizing selection favors the intermediate phenotype.
A birthweight of 7-8 lbs. is
favored.
Heavier and lighter birthweights
are selected against.
– Disruptive selection favors both extreme phenotypes.
Male – more
masculine favored.
Female – more
feminine favored.
Genetic drift
• Random change in allele frequencies that
occur in small populations.
– Founder effect – migration of individuals from a
population
Speciation
• Formation of new species
• Reproductive isolation – two populations
cannot interbreed and produce fertile
offspring
Mechanisms Leading to
Reproductive Isolation
• Behavioral Isolation – differences in courtship
rituals
• Geographic Isolation – natural barrier
– lake or mountain
• Temporal Isolation – time differences in
breeding
Behavioral, geographic or temporal?
Behavioral, geographic or temporal?
Behavioral, geographic or temporal?