The 2007 Nobel Prize in Medicine or Physiology has been won jointly by three genetic scientists: Dr. Martin Evans from Britain, Dr. Mario Capecchi and Dr. Oliver Smithies, from the U.S. Their research work was done separately but when taken together it made possible the "knockout" mice that are now key to basic medical research.
What are knockout mice? To understand that, we first need to know a few basics of genetics.

Genetics is the study of how living things receive common traits from previous generations. It is a modern field of study with most of the path breaking findings happening in the last 60 years. In 1943 it was discovered that the DNA present in the nucleus of every cell of all living things, was the bearer of all genetic information. The DNA molecule is in the form of a twisted ladder which scientists call a “double helix”. To fit into the cell, the twisted, long DNA wraps itself around some proteins. These proteins are packed tightly together until they form a chromosome.

Human cells contain two sets of chromosomes, one set inherited from the mother and one from the father. Thus each cell has 46 chromosomes and hence 46 molecules of double-stranded DNA.

A gene is a segment of a DNA molecule that determines a characteristic in an organism Each gene contains a particular set of instructions that starts a particular growth.

If the gene is normal, the right kind of proteins are made. However, if the gene is changed or ‘mutated’, changes result in the protein they make.

The information contained in our genes is so critical that simple changes or mutations can lead to severe inherited diseases and make us more inclined to chronic or infectious diseases. Scientists believe that most diseases are related in some way to our genes.

In molecular biology, mice are used extensively for research because they share many common genetic features with humans. Mice are also small and easy to maintain. They have short life span and reproduce rapidly which makes them best suited for study.

A knockout mouse is a genetically engineered mouse that has had one or more of its genes made inactive through a gene knockout. Knockout is a route to learning about a gene that has an unknown or incompletely known function. By eliminating the gene and studying the mouse for any resulting differences, researchers try to guess the probable function of that gene.

Dr. Evans laid the groundwork for making the knockout mice when he discovered that days-old embryos are made up of super-powerful cells now known as embryonic stem cells. Each one of the cells has the power to give rise to all the cells and tissues in an animal. Dr.Evans isolated these cells, figured out how to genetically interfere with the cells and implant the altered embryos into foster mothers.

Scientists Mario Capecchi and Oliver Smithies independently developed precise ways to disable or knock out, a single chosen gene.