Chapter 3: Evolutionary genetics of natural populations

What are evolutionary forces?

Processes that change allele frequencies in a population (mutation

Why do evolutionary forces affect genetic variation?

Because changing allele frequencies changes the level of genetic diversity

What does allele frequency change mean?

Some alleles become more common while others become rare or disappear

What is mutation?

A random change in DNA that creates new alleles

Why is mutation important?

It is the only source of new genetic variation

Does mutation strongly change allele frequencies?

No

What is gene flow?

Movement of genes between populations through migration

Effect of gene flow on variation?

Increases variation within populations and makes populations more similar

Example of gene flow?

An individual moves to another population and introduces new alleles

What is natural selection?

Individuals with certain genotypes survive and reproduce more

Effect of selection on allele frequencies?

Beneficial alleles increase and others decrease

Effect of selection on variation?

Often reduces variation because certain alleles are favoured

What is genetic drift?

Random changes in allele frequencies

When is drift strongest?

In small populations (low Ne)

Effect of drift on variation?

Loss of alleles and reduced genetic diversity

How does mutation affect variation?

Adds new alleles and increases variation

How does migration affect variation?

Introduces alleles from other populations and increases variation

How does selection affect variation?

Reduces variation by favouring certain alleles

How does drift affect variation?

Randomly removes alleles and reduces variation

What are discrete traits?

Traits with clear categories

Example of a discrete trait?

Blood type or flower colour

Genetic basis of discrete traits?

Usually controlled by one or a few genes

What are quantitative traits?

Traits that vary continuously

Example of a quantitative trait?

Height or body size

Genetic basis of quantitative traits?

Many genes plus environmental influence

Why are quantitative traits harder to analyse?

Because they are influenced by many genes and the environment

What is genotype-by-environment interaction (GxE)?

The effect of a genotype depends on the environment

Example of GxE?

The same genotype produces different traits in different environments

Why is GxE important?

It determines how traits are expressed under different conditions

Why is GxE important for conservation?

Species may respond differently to environmental changes

What is fitness?

The reproductive success of an individual

Why is fitness important?

It determines which alleles increase through selection

What is directional selection?

One extreme trait is favoured

What is stabilizing selection?

Intermediate traits are favoured

What is disruptive selection?

Both extreme traits are favoured

How do evolutionary forces and traits connect?

Forces change allele frequencies which influence traits and adaptation

How does everything in this lecture connect?

Evolutionary forces change allele frequencies which determine variation influence traits interact with environment and affect adaptation

How do evolutionary forces influence genetic variation?

Mutation introduces new alleles migration adds alleles selection favours certain alleles and drift randomly changes allele frequencies shaping genetic variation