Nobel laureate Mario Capecchi describes work in gene targeting, for which he shares the international award, in simple terms.

What he and his lab accomplished, he said, "is the ability to change a gene in a living mammal. Our patient is the mouse."

They can change any gene, disabling or enabling it. The manipulations are carried out in embryonic stem cells, then it's reintroduced to the mouse, where it's incorporated by the germ cells — sperm and eggs — so that the desired change is reliably passed on to a new generation of mice.

"Then we look at the mouse and say, 'that's what happened,"' when the gene was manipulated, Capecchi said.

Many diseases are either caused by genes or influenced by them, so the ability to study what happens with those genes has great importance. "We can model any disease in a mouse" and study the pathology at different stages. That, in turn, can lead to effective treatments.

In the early days of the research, they had to work with many, many mice to get the desired results. Now, they can not only reliably change the gene but also control where the function change occurs. So they can change a gene's function within the liver if they want to study liver disease, for example, without affecting other parts of the body.