Final answer:
Barbara McClintock was the first researcher to propose the concept of transposons through her work on maize genetics. Transposons, or 'jumping genes', are DNA segments that can move within the genome, affecting gene expression and regulation.
Step-by-step explanation:
The first researcher to propose the existence of transposons in genomes was Barbara McClintock. Through her work on maize genetics during the 1930s, 1940s, and 1950s, she discovered what she referred to as "jumping genes", now known as transposons. These are mobile segments of DNA that can change their position within the genome. McClintock's pioneering research initially did not gain traction within the scientific community, but the concept of transposons was later confirmed and recognized across various organisms including bacteriophages, bacteria, and fruit flies (Drosophila).
Transposons are composed of DNA that can shift location. This movement can influence gene regulation, protein expression, and even an organism's virulence. McClintock's discovery was pivotal in understanding the dynamic nature of the genome and the complexity of genetic regulation, concepts that were far ahead of their time considering the limited molecular technologies available during her research.