On 25th November 2018, Jiankui He, a professor from the South University of Science and Technology of China released a video on YouTube© announcing the birth of twin girls he claimed to have performed ‘gene surgery’ on to prevent HIV infection. The news exploded on media with comments of disbelief, censure and some cautious appreciation from the scientific community as well as the public. So, what is ‘gene surgery’ and what is the controversy about? We carry, in each of our trillions of cells, a copy of the human genome. The genome is made of DNA, a very long polymer made of pairs of four chemical building blocks (denoted by the letters A, T, G and C). It is this very precise sequence of A, T, G and C, all 3 billion pairs of them that we call the human genome. Changes in this sequence lead to the interesting differences between each of us. But, these changes also may result in mutations that cause diseases. These changes in the DNA sequence happen as DNA is ...