Assumed audience
General adult who has completed Cells and Metabolism.
DNA structure
DNA is a double helix of nucleotide bases (A, T, G, C) (DNA). The sequence of bases encodes genetic information. DNA replication copies this information before cell division.
Genes and proteins
A gene is a segment of DNA that encodes a functional product — usually a protein. The flow of information goes: DNA → RNA → protein (the “central dogma”). Proteins carry out most of the work in cells: as enzymes, structural components, signals, transporters.
Heredity
When organisms reproduce, they pass copies of their DNA to their offspring. Sexual reproduction combines DNA from two parents, producing genetically unique offspring. This is the basis of heredity — why offspring resemble but are not identical to their parents.
Mutation and variation
Errors in DNA replication produce mutations — changes to the DNA sequence. Most mutations are neutral or harmful, but some produce beneficial new traits. Mutation is the ultimate source of all genetic variation.
Natural selection
Organisms with traits better suited to their environment tend to survive and reproduce more successfully (natural selection). Over generations, this differential reproduction changes the genetic composition of populations. Beneficial traits become more common; harmful traits become less common.
Evolution
The change in the genetic composition of populations over generations (evolution). Natural selection is the primary mechanism, but genetic drift, gene flow, and mutation also contribute. Evolution produced all the diversity of life from common ancestors over roughly 3.8 billion years.
Adaptation
A trait that has been shaped by natural selection (adaptation). The woodpecker’s skull, the cactus’s water-storing tissue, the Arctic fox’s white winter coat — all adaptations to specific environments.
Why this matters
Genetics and evolution explain both the unity and the diversity of life — why all organisms share basic molecular machinery, and why they differ in form and function.