Recombinant Proteins are expressed in:

The correct answer is Option (2) → Heterologous Host

Option (1) Cloning vector — Incorrect. A cloning vector, such as a plasmid, carries the gene into the host. The protein is made by the host cell, not by the vector.

Option (2) Heterologous Host — Correct. A heterologous host is an organism of a different species from the source of the gene, such as E. coli making human insulin. A protein made this way is a recombinant protein.

Option (3) Homologous chromosomes — Incorrect. Homologous chromosomes are the pairs of matching chromosomes in a diploid cell. They are not a place where proteins are expressed.

Option (4) Promotor — Incorrect. A promoter is the DNA sequence where RNA polymerase binds to start transcription. It is part of a gene, not a host.

NCERT Extract:
Obtaining the Foreign Gene Product – “… After having cloned the gene of interest and having optimised the conditions to induce the expression of the target protein, one has to consider producing it on a large scale. … If any protein encoding gene is expressed in a heterologous host, it is called a recombinant protein.”