Final answer:
The mobile gene in Barbara McClintock’s corn experiments was the Ds (Dissociator) gene. Its movement, which disrupted other genes like Bz, was a demonstration of transposons. This discovery earned McClintock a Nobel Prize.
Step-by-step explanation:
Discovery of the Mobile Gene in McClintock's Corn Experiments
The gene that was mobile in Barbara McClintock’s experiments with mutable sites in corn was the Ds gene. In her renowned studies, McClintock discovered that the Ds gene, also known as the dissociation locus, was capable of moving and could cause breakage in the chromosome where it resided. The movement of the Ds gene was dependent on the presence of another gene called Ac, or activator.
McClintock's groundbreaking work revealed that the Ds gene could insert itself into or near other genes, thereby affecting their function. For example, when the Ds gene inserted itself into the Bz gene responsible for purple color in corn kernels, it disrupted the Bz gene's function, leading to colorless kernels. This movement and the subsequent alteration in gene activity are characteristic of transposons, mobile pieces of DNA that McClintock was the first to identify in eukaryotic organisms, which earned her the Nobel Prize in Physiology or Medicine in 1983.