A genome is the complete set of DNA that contains all of the instructions for building, maintaining, and running an organism. Every organism has a distinct genome. There is a human genome, a dog genome, a daisy genome, and so on.

A genome includes all of an organism's genes. It's all of the DNA that tells each of the cells of that organism when, where, and at what level to turn on each gene—and much, much more. One way to think about a genome is as a giant recipe book with directions to create another life form.

What Is a Genome Project?

A genome project is a research effort to sequence the DNA and identify the genes that belong to an organism. Sequencing the DNA means figuring out the order of the bases, or building blocks, in the DNA—the order of steps or letters in that genome recipe book.

One example of a genome project is the Human Genome Project (HGP), which was an international collaboration that ran from 1990-2003. It successfully sequenced most of the 3.2 billion base pairs of the human genome, at a cost of around $3 billion. Over a decade-and-a-half later, the same can be done in a matter of days for $1,000 or less.

Another example is The Cancer Genome Atlas (TCGA). The goal of this project was to determine the genetic mutations associated with cancer, both in genes and outside of genes.

It’s important to note that even when the first human genome was published, it was only mostly complete. There were still many gaps that existed where scientists weren't able to fully assemble the DNA sequence. It took almost another 20 years before the remainder of the human genome was fully assembled as part of the Telomere-to-Telomere Consortium effort, in March 2022.

Genome vs. Gene

A genome is the complete set of DNA that has the instructions for a living thing, while a gene is one of the many instructions that it takes to build, run, and maintain a living thing.

Going back to the recipe book analogy, one way to think of the relationship between a genome and a gene is to imagine that the genome is a recipe book and that each gene is one of the recipes in the book.

What Is Genome Mapping?

Like its name implies, genome mapping creates a map of the genome. It makes it easier for researchers to find what they are looking for. It is different from a genome sequence in that it is less detailed.

For example, a genome map might map out where each of the 20,000 or so human genes are located instead of laying out all 3.2 billion base pairs. This makes it easier for researchers to find genes they are interested in.

The two main types of genome maps are linkage maps and physical maps. A linkage map shows the relative positions of genes based on how frequently they're inherited together. A physical map, on the other hand, shows exactly where the genes are located in a genome.

How Many Base Pairs Are There in the Human Genome?

The human genome has just over 3 billion DNA base pairs made up of four types of bases: thymine (T), adenine (A), guanine (G), and cytosine (C). Because most human cells have two copies of the human genome, most cells have over 6 billion base pairs. If you were to print out all of the base pairs in the genome, it would fit into 200 phone books with 500 pages each.

How Is Genomics Different from Genetics?

Genomics looks at all the genes or DNA in an organism. But genetics usually focuses on a single gene. An example of genomics would be how AncestryDNA^® uses someone's DNA to figure out where their ancestors came from or what traits they might have inherited. However, an example of genetics would be a study that looks at how changes in one gene might influence someone's risk for getting breast cancer or sickle cell anemia.

Learn more about how the AncestryDNA^® test works and what you can expect from your test results.