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40,000

Drosophila melanogaster (fruit fly)

3,500

40,000

Xenopus laevis (toad)

15,000

200,000

Mus musculus (mouse)

25,000

150,000

Source: Data from B. L. Lewin, Genes V (Oxford: Oxford University Press, 1994), p. 536.

Source: Data from B. L. Lewin, Genes V (Oxford: Oxford University Press, 1994), p. 536.

days. This rate is possible because replication takes place simultaneously from thousands of origins.

Typical eukaryotic replicons are from 20,000 to 300,000 base pairs in length (Table 12.1). At each replication origin, the DNA unwinds and produces a replication bubble. Replication takes place on both strands at each end of the bubble, with the two replication forks spreading outward. Eventually, replication forks of adjacent replicons run into each other, and the replicons fuse to form long stretches of newly synthesized DNA (I Figure 12.6). Replication and fusion of all the replicons leads to two identical DNA molecules. Important features of theta replication, rolling-circle replication, and linear eukaryotic replication are summarized in Table 12.2.

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