Functional expression refers to the process of expressing and studying the function of a gene or protein in a host organism, typically in a laboratory setting. This research area is important for understanding the role of specific genes or proteins in various biological processes, as well as for developing new therapies or applications in areas such as medicine, biotechnology, and agriculture. Functional expression often involves using recombinant DNA technology to introduce the gene of interest into a host cell or organism, and then measuring the effects of the expressed gene on the host's physiology or biochemistry. Overall, functional expression research helps to elucidate the mechanisms underlying biological processes and can lead to important advancements in biotechnology and medicine.