Eye of the tiger

In 1994, at the same time the genomic era was beginning, Walter Gehring and colleagues at the University of Basel carried out a Frankenstein experiment par excellence: they were able to turn on a gene called eyeless in various places on the body of the fruitfly, Drosophila melanogaster. The result was amazing – fruitflies that had whole eyes sprouting up all over their bodies. Scientists refer to genes such as eyeless as master regulatory genes (note that genes are often named after the problems they cause when mutated). These master regulatory genes produce proteins that control large cascades of other genes, like those needed to produce complex features such as eyes; eyeless controls one such cascade that contains more than 2000 other genes. Turning it on anywhere in the body activates the cascade and produces a fully formed, but non-functioning, eye.

• Sequence similarity and homology

• Global and local alignments

• Statistical significance of alignments

• BLAST and CLUSTAL

It turns out that all multicellular organisms use master regulatory genes, often for the same purpose in different species. Slightly different versions of the eyeless gene are used in humans, mice, sea squirts, squids, and, yes, tigers, to control eye formation. We call these different versions of the same gene homologs, to denote their shared ancestry from a common ancestor.