Final answer:
Barbara McClintock's discovery of transposons in maize revolutionized genetics by highlighting the mobility of DNA segments within the genome.
Explanation:
The fourth great discovery of genetics is the identification of transposons, which are mobile segments of DNA that can move within an organism's genome. Barbara McClintock conducted groundbreaking work on maize genetics in the 1930s through 1950s, leading to the discovery of transposons. A transposon is a gene that can jump from one genomic site and insert into another, thereby regulating gene expression and causing mutations.
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