A genome is the complete set of DNA in an organism. In humans, it includes nearly all genetic material in the nucleus, organised into chromosomes, plus a small mitochondrial genome.
What this means in practice
A genome is broader than a single gene or a small panel of genes. It includes coding and non-coding DNA, structural regions, regulatory regions, and many sequences that affect how genes are used.
This matters because genome sequencing looks across the full DNA set rather than focusing on one small part. That approach is relevant in rare disease, cancer, ancestry, and research, where important information may lie outside well-known genes.
How a genome is organised
The key hierarchy is:
DNA → genes and non-coding regions → chromosomes → genome
DNA is the material itself. Genes are specific stretches of DNA with functional roles. Chromosomes are large packaged DNA structures. The genome is the full collection of all that DNA.
In humans, most of the genome sits in 23 chromosome pairs in the nucleus. A small additional genome is found in mitochondria.
Genes are only part of the genome
A common mistake is to treat genome and gene as if they mean the same thing. They do not. Genes make up only part of the genome.
Much of the genome does not directly code for proteins. Some non-coding regions regulate when genes are active. Others have structural, evolutionary, or still incompletely understood roles. This is why whole-genome thinking is broader than gene-by-gene thinking.
A concrete example
CFTR is one gene. It sits on chromosome 7. Chromosome 7 is one part of the human genome.
That example shows the scale difference clearly. A gene is one defined region. A chromosome contains many genes and other DNA. The genome contains all chromosomes together, plus mitochondrial DNA.
Details that matter
- A genome is broader than a gene.
- The genome includes non-coding DNA, not only genes.
- Human genomes are highly similar to one another, but not identical.
- A reference genome is a shared coordinate system and sequence representation, not one perfect person.
- Whole-genome sequencing reads DNA across the genome rather than only the protein-coding exome.
Common mistakes
Frequent misunderstandings include:
- using genome and gene interchangeably
- assuming only genes matter biologically
- assuming the reference genome represents a perfect or normal human genome
- assuming different cell types usually have different genome sequences
- assuming non-coding DNA is biologically irrelevant
Genome vs exome
The genome includes essentially all DNA. The exome is the subset that mainly covers protein-coding exons.
This distinction matters because exome sequencing can miss important variants outside coding regions, while whole-genome sequencing covers a broader range of possible findings.
Why people encounter this term
Most readers meet the term genome in one of these contexts:
- whole-genome sequencing
- discussions of inherited disease
- ancestry and population genetics
- articles about the human genome or reference genome
In all of these settings, genome means the full DNA set, not one specific gene.
Related pages
Reference
National Human Genome Research Institute. Talking Glossary of Genomic and Genetic Terms: Genome.
https://www.genome.gov/genetics-glossary/Genome
