Which enzymes are commonly used in genetic engineering? 

Restriction endonuclease and ligase

The answer to the question "Which enzymes are commonly used in genetic engineering?" is (c) Restriction endonuclease and ligase.

1. Restriction endonucleases: These enzymes are also known as restriction enzymes. They act as molecular scissors and can recognize specific DNA sequences (known as recognition sites) and cut the DNA at those sites. Different restriction enzymes cut DNA at different recognition sites. This property allows scientists to precisely cut DNA at specific locations.
2. Ligase: DNA ligase is an enzyme that can join or "ligate" DNA fragments together. After the DNA is cut by restriction enzymes, ligase is used to seal the gaps and connect the DNA fragments. This process is essential in creating recombinant DNA molecules, where DNA from different sources is combined.

Other enzymes that are commonly used in genetic engineering include:

• DNA polymerase: This enzyme is used to synthesize DNA. It is essential for DNA replication and for the repair of damaged DNA.
• Reverse transcriptase: This enzyme is used to synthesize DNA from RNA. It is used in the study of gene expression and in the development of HIV treatments.
• Alkaline phosphatase: This enzyme is used to remove phosphate groups from the ends of DNA fragments. This is necessary before DNA fragments can be ligated together.

These enzymes are used in a variety of genetic engineering techniques, such as cloning, gene editing, and gene therapy.