440 Chapter 13 • The Dynamic Genome: Transposable Elements several distinct chromosome locations. None appears ex-actly at the normal locus of the rosy gene. These new ry + genes are found to be inherited in a stable fashion. Because the P element can transpose only in Drosophila, these applications are restricted in their usage. In contrast, the maize Ac element is able to transpose af-ter its introduction into the genomes of plant species in-cluding the weed Arabidopsis, lettuce, carrot, rice, barley, and many more. Like P elements, Ac has been engineered by geneticists for use in gene isolation by transposon tag-ging. In this way, Ac, the Frst transposable element discov-ered by Barbara McClintock, serves as an important tool of plant geneticists more than 50 years later. matically in eukaryotes and did not correlate with bio-logical complexity. ±or example, the genomes of salaman-ders are 20 times as large as the human genome, whereas the genome of barley is more than 10 times as large as the genome of rice, a related grass. The lack of correlation between genome size and the biological complexity of an organism is known as the C-value paradox. Barley and rice are both cereal grasses and as such
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