The second half of the 20th century was witness to incredible advances in molecular biology and computer technology. Only 50 years after identifying the chemical structure of DNA (1953), the sequence of the human genome has been determined and can be downloaded to a computer small enough to fit in your hand. The pace of science can be truly dizzying. So what do you do when you literally have the book of life in the palm of your hand? Well, you read it of course. Unfortunately, it's much easier to read the book of life than to understand it, and one of the great quests of the 21st century will be unraveling its mysteries. One particularly fruitful approach to deciphering the book of life has been through comparative studies, such as those between mouse and human.
Comparisons between the human and mouse genomes show how little has changed since humans and mice last shared a common ancestor around 75 million years ago. Very few genes are unique to humans or mice, and in general the genes are more than 80% identical at the sequence level. However, genes account for a small fraction of these genomes and the majority of sequence is not recognizably similar. This is where BLAST, the Basic Local Alignment Search Tool, comes in. BLAST is useful for finding similarities between biological sequences, be they DNA, RNA, or protein. Sequence similarity is often an indication of conserved function, and you can use comparative sequence analysis to understand biological sequences in much the same way that ancient Greeks used comparative anatomy to understand the human body or that linguists used the Rosetta Stone to understand Egyptian hieroglyphs.