Lewis Wolpert: All praise to our brother the fruit fly

Scientists were astonished when they realised that many of the key genes that control the embryonic development of fruit flies have analogous genes in humans that play a remarkably similar role in our own development in the womb. The prime example is the so-called "hox" genes, which are active at an early stage in the growth of both fly and human embryos. In humans, hox genes determine where our ribs will develop and in the flies where the head, thorax, and abdomen grow.

A major figure in this discovery is Janni Nusslein-Volhard from the Max Planck Institute in Tubingen, Germany, who was one of a trio awarded the Nobel Prize in 1995. I recently went to her 60th birthday celebrations in Tubingen. What is it about her that led to such important discoveries, particularly as women do not always have an easy time in science?

Nusslein-Volhard had the right qualities for scientific investigation, and she was prepared to take risks. When she finished her degree in molecular biology on mechanisms relating to nucleic acids she took six months off to decide what she really wanted to achieve in life – the genetics of the fruit fly, Drosophila. With Eric Wieschaus, she developed a way of screening key genes controlling the embryo's development by chemically inducing mutations in these genes and then searching flies for abnormalities in the embryo. Their work changed the face of genetics and developmental biology. She then did the same for the zebra fish, now an animal model of embryonic development.

There are some unexpected features about the development of flies that are now recognised as fundamental to the way genes control the behaviour of cells in the developing embryo. Early in the development of the fly, a group of genes are turned in a series of 14 stripes and these outline the future segments of the larva and adult. These so-called "pair-rule" genes are expressed in every second stripe. So the gene "even-skipped" is expressed in the seven odd-numbered stripes, while others are expressed in the seven even-numbered stripes. When this pattern of stripes was first seen, the mechanism proposed to explain the pattern was based on an underlying wave, with the stripes being expressed at the peaks and troughs.

But there is no wave, and each stripe is specified independently. The gene even-skipped has a control region that looks at the local concentration of proteins and this correctly determines that the gene is active in each of its locations. Some parts of the control region will respond negatively to these proteins, while others will treat it as a positive signal. The ability of the control region of a gene to integrate local information and so determine if the gene is to be active or inactive is a fundamental feature of development. It is these control regions that make us so different from our ape relatives. All praise to Nusslein-Volhard and her flies.

The writer is Professor of Biology as Applied to Medicine at University College, London