Mary-Claire King has argued that all young women should be screened for the known breast-cancer risk mutations

You probably dont recognise the name Mary-Claire King, but Im willing to bet you know this extraordinary womans work. King, a professor at the University of Washington, did her PhD with Allan Wilson in evolutionary genetics, and together they were the first to show that human and chimp are about 99 per cent identical at the DNA level.

In 1974, King took the evolutionary genetics insights she had learned during her PhD and applied them to a different problem. She started searching for genetic determinants of breast cancer. Next month, October 2014, is the 20th anniversary of the mapping of the first breast cancer gene.

Forty years ago, the landscape of genetics research was markedly different from today. There was not yet a single human genetic disease mapped. It was nine years before the first one, responsible for Huntingtons Disease, was linked to a specific chromosome. There was no genome sequence to look up, not even an accurate idea of how many genes are in the human genome. Many scientists thought there were as many as 100,000 genes, but the true value is closer to a humbling 22,000.

Given these scientific challenges, the best approach available to King and her research team was to use a technique called linkage mapping.

This takes advantage of the fact that as chromosomes are passed from parent to child, getting scrambled through the generations, genes that are physically close neighbours on a chromosome are more likely to stay together, unscrambled. Using this genetic insight, characteristics in this case increased susceptibility to breast cancer can be tested for proximity to known landmarks in the genome based on patterns of co-inheritance.

This work is slow and painstaking and, for about 16 years, King and her relatively small research team were working on this alone. By 1990 they had narrowed down the location of a breast cancer gene (dubbed BRCA1 by King) to a comparatively small region on chromosome 17.

To give an impression of what they had done, it was as if the total length of the genome was the road from Galway to Sligo, and Kings research had narrowed down the search to Tuams main street.

At this point, the goal was in sight. Others decided to join the search in competition with King. This was dubbed the race by many commentators. More than 100 researchers were working full tilt in about a dozen labs around the world.

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Heres to the geneticist who helped map the first breast cancer gene