To nobody's surprise, therefore, though the mutant fly is capable of learning things, it forgets them within minutes.

ECONOMIST: Memory formation

When geneticists replaced one of the mutant fly genes by its homologous mouse gene the fly developed normal flies' eyes and not mouse eyes.

ECONOMIST: Genetic science

This is a rare brain disorder that is caused by an autoimmune response which destroys the human equivalents of the ion channels that are affected in the mutant fruit fly.

ECONOMIST: Memory formation

With the help of Chiara Cirelli, who also works at the University of Wisconsin, Dr Tononi has created a mutant fruit fly that sleeps only two or three hours a night. (A normal fly sleeps between eight and 14 hours.) The mutation itself is in a gene for a nerve-cell protein of a type known as an ion channel.

ECONOMIST: Memory formation

He located the mutant gene responsible for this monstrosity on one of the fly's chromosomes.

ECONOMIST: Genetic science