genome sequencing

Genome sequencing is reading out the entire instruction manual of an organism, letter by letter. The goal is to determine the order of the four DNA bases — A, C, G, and T — across all the chromosomes that make up that organism's genome.

Because no machine can read a whole genome in one continuous pass, the DNA is broken into many small pieces, each piece is sequenced, and the overlapping fragments are then computationally stitched back together — a process called assembly. The result is a long string of bases that represents the genome.

Sequencing a genome is the starting point, not the finish line. A raw sequence still has to be assembled, checked for errors, and annotated before it tells you where the genes are and what they might do. Modern projects often combine several sequencing technologies to get both accuracy and the ability to span long, repetitive regions.