In the early 1990s, Carolyn Napoli and her colleagues were working on petunias, attempting to genetically engineer a variety with dark purple petals by introducing numerous copies of a gene that encodes purple pigment in the flower petals (C. Napoli, C. Lemieux, and R. Jorgensen. 1990. Plant Cell 2:279–289). Their thinking was that extra copies of the gene would cause more purple pigment to be produced and would result in a petunia with an even darker hue of purple. However, much to their surprise, many of the plants carrying extra copies of the purple gene were completely white or had only patches of color. Molecular analysis revealed that the amount of mRNA produced by the purple gene was reduced 50-fold in the engineered plants compared with wild-type plants. Somehow, the introduction of extra copies of the purple gene silenced both the introduced copies and the plant’s own purple genes. Provide a possible explanation for how the introduction of numerous copies of the purple gene silenced all copies of the purple gene.
In the early 1990s, Carolyn Napoli and her colleagues were working
on petunias, attempting to genetically engineer a variety with dark
purple petals by introducing numerous copies of a gene that encodes
purple pigment in the flower petals (C. Napoli, C. Lemieux, and R.
Jorgensen. 1990. Plant Cell 2:279–289). Their thinking was that extra
copies of the gene would cause more purple pigment to be produced and
would result in a petunia with an even darker hue of purple. However,
much to their surprise, many of the plants carrying extra copies of the
purple gene were completely white or had only patches of color.
Molecular analysis revealed that the amount of mRNA produced by the
purple gene was reduced 50-fold in the engineered plants compared with
wild-type plants. Somehow, the introduction of extra copies of the
purple gene silenced both the introduced copies and the plant’s own
purple genes. Provide a possible explanation for how the introduction of
numerous copies of the purple gene silenced all copies of the purple
gene.
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