Genomics is the field of genetics that studies genomes rather than individual genes. With the advent of modern DNA sequencing technology, biologists can identify and study genomes, meaning the entire genetic code of an individual organism. When the human genome was first sequenced in 2000, scientists discovered that genetic sequences can contain vast amounts of data.
Although a genome is the complete genetic sequence of a single organism, it is composed of more than genes. There are many regions in a specific gene that determine when it is active. Other regions have either unknown functions or no function at all.
Complex organisms like humans have very large genomes. For example, if you converted the names of DNA nucleotides in the human genome to the first letter of their names and printed all of the letters on paper, the book you’d get would be about a million pages long.
Sequencing a whole genome is a formidable task. Advances in technology have decreased sequencing costs significantly. In early 2012, two biotechnology companies predicted they would soon be able to sequence an entire human genome in little more than a day for a cost of about $1,000. When this occurs, doctors might routinely order genome sequencing services, which could prove especially useful in the treatment of cancer and the study of disease.
By itself, genome sequence information is not useful. It’s like owning a book but not knowing how to read. To make the information useful, you need to know which regions of the genome are functional and what they do.
Biologists use several approaches to study gene function. For example, they might use a microarray to measure the activity of a large number of different genes in certain cell types. Microarrays are collections of microscopic spots of DNA attached to a solid surface. Biologists can treat many of these spots with reagents to get rapid results from many samples at once.
Analyzing messenger RNA (mRNA) in cells also helps biologists identify genes that provide instructions for the production of specific proteins. Researchers can compare DNA from individuals with and without a specific disease to identify regions in a gene that might play a role in that disease. Or they can build genetic maps, which locate genes based on their position relative to genetic markers — that is, nucleotide sequences whose positions are already known.
Comparative genomics is another interesting area of research. In this field, scientists compare genome data from different species such as humans and chimpanzees. This information enables scientists to learn more about human evolutionary history. Sometimes, these comparisons prove useful to medical research by revealing more about the function of specific regions of the human genome. Often scientists can identify the function of a gene in organisms such as yeast by performing experiments that would impossible or unethical in humans.