Genomics

Genomics is the reading and study of the complete DNA of a living thing, such as a person, a tumour or a germ. DNA is a long chain of four chemical letters, written A, C, G and T. A person's DNA holds about three billion of these letters. The order of the letters carries the instructions for building and running the body. Reading that order is called sequencing. Genomics now guides cancer treatment, infection tests and the search for new drugs.

Here is how it works in general. A sample is taken, such as blood, saliva, a piece of a tumour or a swab with a germ in it. The lab extracts the DNA and cuts it into millions of short pieces. A DNA sequencer reads the letters of each piece. Software then lines up the pieces against a reference genome, a standard version of the DNA that everyone uses for comparison. Next it lists the places where this sample is different. Each difference is called a variant. Most variants are harmless. Specialists, with the help of large databases, decide which few matter, for example a variant known to make a cancer grow.

Most of the work is in software. One person's genome produces hundreds of gigabytes of raw data, and engineers build the pipelines that store, align and compare it. In India, a national project called GenomeIndia has sequenced the genomes of thousands of Indians, because the reference data from other countries does not show all the variants that are common here.

Take, for example, a patient with lung cancer. Tumour genomic profiling reads the cancer's genes, and the doctor may choose a medicine that targets the one variant that drives this cancer.

Consider a patient with a long-lasting cough. A molecular test system finds the DNA of the tuberculosis germ in the sample in under two hours, and also checks for the variant that makes the germ resistant to a main TB drug.

Say a scientist wants to know which genes a disease switches on. RNA sequencing analysis reads which genes are active in diseased cells and in healthy cells, and shows the differences.

How is genomics different from genetics? Genetics usually studies one gene at a time, and how it passes from parents to children. Genomics reads the whole genome at once, and compares millions of letters across many people. A person's genome is also among the most sensitive personal data, so it is protected under data protection law.