Final answer:
Transposons discovered in maize by Barbara McClintock are DNA elements that can move within a genome to create diversity and affect gene regulation. They have a unique structure, are capable of both 'cut-and-paste' and 'copy-and-paste' transposition, and have evolutionary significance, contradicting the idea that they are simply 'junk DNA'.
Step-by-step explanation:
Transposable Genetic Elements in Maize
Transposable genetic elements, or transposons, observed in maize by Barbara McClintock, have significantly shaped our understanding of genetics. These "jumping genes" have the unique ability to move from one location to another within the genome. Equipped with special inverted repeat sequences and a gene encoding the enzyme transposase, transposons can either excise and integrate elsewhere (cut-and-paste) or replicate themselves in a new location (copy-and-paste). This process, known as transposition, introduces genetic diversity and can affect gene regulation, potentially altering phenotypes. Despite originally being met with skepticism, transposons are now recognized to contribute to evolutionary adaptation and diversity, and are not considered merely 'junk DNA'.
Moreover, the discovery of transposons in maize has opened up our understanding of horizontal gene transfer, a mechanism through which transposons can spread between species. This has profound implications for evolutionary biology and the study of genetic regulation, proving that transposons have beneficial roles in genomes beyond their own replication.