Genome editing

Genome editing is a type of genetic engineering.
DNA is inserted, replaced, or removed from a genome using artificially engineered nucleases, or "molecular scissors". The nucleases make specific double-strand breaks (DSBs) at desired places in the genome. The cell’s own mechanisms repair the induced break(s) by natural processes. 
At present there are four families of engineered nucleases being used.
To understand the function of a gene or a protein one interferes with it in a sequence-specific way, and watches its effects on the organism. However, in some organisms it is difficult or impossible to do site-specific mutation. Therefore more indirect methods have to be used. Examples are: 
Genome editing was chosen by Nature Methods as the 2011 Method of the Year. The technique is already being used, but implanting modified embryos into a woman is not yet permitted.
The CRISPR/Cas9 method.
In 2017 this system was announced as one of the biggest scientific achievements of the year. Cas9 is an enzyme which, with a guide RNA, can put a new sequence of DNA into a genome. Sir John Skehel said "That might allow you to knock out a particular gene in a cell, or introduce a particular gene, or correct a particular mutated gene that you want to work better".