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Lecture 8

BIO120H1 Lecture Notes - Lecture 8: Stabilizing Selection, Crypsis, Experimental Evolution

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Spencer Barrett

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BIO 120 Lecture 8 Notes
Relative genetic contribution of individuals to next generation as
a result of dierences in viability and fertility
Selective advantage
Some individuals better adapted to the environment and thus
have higher $tness
Any trait that contributes to $tness by making an organism
better able to survive or reproduce in a given environment
The evolutionary process that leads to the origin and
maintenance of such traits
Arti$cial selection
Domesticated plant and animals
Selection experiments in genetics
Selection by humans
Has a purpose or goal (want to increase productivity)
Natural selection
All organisms
Selection by abiotic and biotic environment
No purpose or goal
Simply a blind mechanistic process with no foresight
Types of natural selection on quantitative traits (how does it aect the
means and variant of the trait)
Stabilizing selectionevolution is occurring , there is an actual
selection, but the mean does not change (favors average traits)
Directional selection the whole distribution shifts to match the
favored traits (favors one extreme)
Disruptive selection diverging and lead to speciation (favors
both extremes)
Stabilizing selection on human birth weight
Small birth weight cannot survive
Large birth weight cannot born
Directional selection of beak size in Galapagos $nches
At seed abundance decreased, the population fell
At seeds became harder, the average beak size increased
Disruptive selection on beak size in African $nches
Disruptive selection leads to character divergence and in some
case many lead to speciation
Requires spatial heterogeneity or discrete resources
The struggle to determine the mechanisms of selection
Today hundreds of measurements of selection demonstrating
$tness dierences and evolutionary change in traits
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