Which genetic mechanism did McClintock demonstrate in maize?

Which genetic mechanism did McClintock demonstrate in maize?

• A. Crossing over
• B. Mutation
• C. Polyploidy
• D. Transposition

Answer: (D)

Transposable elements—the moving pieces of DNA within the genome—are the key idea here. Barbara McClintock showed that in maize, genes could be disrupted or restored not by a one-time mutation, but by pieces of DNA that physically jump from one chromosome location to another. She used the kernel color system, where the Ds element can insert into pigment genes and block their function, producing colorless patches, and then can excise and leave the gene functional again, restoring color in new spots. This movement depends on the Ac element, which provides the necessary enzyme to cut and paste these elements. This evidence reveals genome dynamism: genetic function can change location and affect traits without requiring standard recombination during meiosis or a fixed single-base change. It’s distinct from crossing over, which exchanges chromosome segments between homologs; from polyploidy, which is a whole-genome duplication; and from simple mutation, which doesn’t capture the idea of a DNA segment actively relocating within the genome.

Transposable elements—the moving pieces of DNA within the genome—are the key idea here. Barbara McClintock showed that in maize, genes could be disrupted or restored not by a one-time mutation, but by pieces of DNA that physically jump from one chromosome location to another. She used the kernel color system, where the Ds element can insert into pigment genes and block their function, producing colorless patches, and then can excise and leave the gene functional again, restoring color in new spots. This movement depends on the Ac element, which provides the necessary enzyme to cut and paste these elements.

This evidence reveals genome dynamism: genetic function can change location and affect traits without requiring standard recombination during meiosis or a fixed single-base change. It’s distinct from crossing over, which exchanges chromosome segments between homologs; from polyploidy, which is a whole-genome duplication; and from simple mutation, which doesn’t capture the idea of a DNA segment actively relocating within the genome.