Genetic engineering is a technique for artificially and deliberately modifying DNA (genes) to suit human needs. It is used to change the genetic makeup of the cells by using Recombinant DNA technology 

Recombinant DNA is the artificially created DNA which incorporates DNA segments from different sources into one.

Restriction endonucleases are specific enzymes which can cleave double stranded DNA at specific sites called recognition sequences. Restriction endonucleases provide protection to the bacteria by restricting the growth of bacteriophages. They also serve as tools for Recombinant DNA technology.

BACs and YACs are artificial chromosomes from bacteria and yeast used for efficient gene transfer and gene sequencing.