1. The Effect of Natural Selection on the Distribution of Alleles in a Population (16.1 – 16.2)

2. Heritable Variation
The number of phenotypes produced for a given trait depends on how many genes control the trait

3. Single gene trait
Is controlled by a single gene with that has two alleles
So, variation in this gene only produces 2 distinct phenotypes

4. Natural Selection -> on a single gene trait
Natural selection on a single-gene trait can lead to changes in allele frequencies and therefore evolution

5. Polygenic traits Traits are controlled two or more genes or alleles
As a result, one polygenic trait can have many possible genotypes and phenotypes
So, their appearance is better represented with a normal population curve

6. Original Population
Normal population distribution based on random breeding and has few individuals at the extremes with many average individuals.
Less hairiness medium hairiness more hairiness

7. Stabilizing Selection
Fine tunes populations, by selecting against both extremes. The average is favoured.
This stabilizes populations.
May be the result of seasonal fine tuning.
Low birth weight medium HIGH birth wght
Which alleles would be very uncommon in this population? More common?

8. Directional Selection
Favours one extreme over the other.
Population shifts in one direction.
May be the result of more permanent climate changes.
Less hairiness medium hairiness more hairiness
How does this alter the relative frequency of alleles in the population?

9. Disruptive Selection
Favours two extremes and selects against the average.
May be the result of the population being separated into two different environments.
Speciation occurs.
Less hairiness medium hairiness more hairiness
How does this alter the relative frequency of alleles in the population?

10. HW / Review: 16-2 Section Assessment P 402 Q# 1 – 2
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