7.3 environmental selection pressures, genetic drift and gene flow

What are the three agents that can cause allele frequencies to change over time?

Changes in environmental selection pressure (natural selection), genetic drift, and gene flow.

What are environmental selection pressures?

External agents which influence the ability of an individual to survive in their environment.

What are examples of physical selective pressures?

Climate change and food shortages.

What are examples of biological selective pressures?

Infectious diseases and predation.

What are examples of chemical selective pressures?

Pollutants within the soil and drugs.

When does natural selection occur?

When any selective pressure acts on a population where random mutations have led to variation.

What is fitness?

The ability to survive and pass genetic material on to the next generation.

What is a selective advantage?

The relative higher genetic fitness of a phenotype compared to other phenotypes controlled via the same gene.

What is evolution?

A change in a gene pool over time.

What is step 1 in the mechanism of natural selection?

Variation exists in the gene pool, created by new alleles from inheritable mutations.

What is step 2 in the mechanism of natural selection?

A struggle for the population to survive occurs as environmental selection pressures act upon them.

What is step 3 in the mechanism of natural selection?

Individuals in the population that are better adapted survive and reproduce.

What is step 4 in the mechanism of natural selection?

Favorable alleles increase in frequency in the gene pool over generations.

What is genetic drift?

Random, unpredictable, non-directional changes in allele frequencies from one generation to the next owing to chance events.

What is the bottleneck effect?

Chance effects on allele frequencies resulting from a major reduction in population size due to a natural disaster or new disease.

How does the bottleneck effect impact genetic diversity?

It reduces genetic diversity because a random event leads to the death and loss of certain alleles.

What is the founder effect?

The formation of a new population from a small, isolated number of individuals.

How do both founder and bottleneck effects affect a population?

They both drastically reduce genetic diversity as a result of decreasing the population size.

What is gene flow?

The movement of individuals and their genetic materials (alleles) between populations via interbreeding.

How do you calculate the change in a population size?

Births minus deaths plus immigration minus emigration.