The theory of evolution is the foundation of modern biology. All new species have developed from existing ones, meaning that all living organisms share a common ancestor. This shared ancestry is represented in phylogenetic classification, where closely related species are grouped based on evolutionary relationships.

Because of this common ancestry, similarities exist across all living things, including:

• Biochemistry: All organisms make proteins using the same ~20 amino acids.

• Cell structures: Similar organelles and cell components.

• Genetic material: DNA is used as the molecule of inheritance.

• Genetic code: The code used to translate genes into proteins is universal.

In this module you will cover:

Genetic Variation Within Populations: All individuals in a species share the same genes, but usually have different versions (alleles) of those genes. These alleles are inherited from their parent(s) which you will study by looking at genetic crosses. Organisms show variation in their phenotypes, which is caused by a combination of genetic factors (different alleles) and environmental influences.

How Allele Frequencies Change: There are two key processes that cause changes in allele frequencies in populations- genetic drift and natural selection. A change in allele frequency over time = evolution.

Speciation and Reproductive Isolation: If a population becomes geographically or reproductively isolated from others there is no gene flow (no mixing of alleles between populations). Over time, genetic differences accumulate in the isolated population. Eventually, individuals from the isolated group may no longer be able to breed successfully with individuals from the original population. This is called reproductive isolation - it marks the formation of a new species.

Communities, Competition, and Ecosystems: Populations of different species live together in communities. These populations show intraspecific and interspecific competition. Each population is affected by biotic factors and abiotic factors. Together, all the biotic and abiotic factors in an area make up an ecosystem - a dynamic, interacting system of life and environment.