Many eukaryotic genes contain coding regions called exons and noncoding regions called intervening sequences or in-trons. For example, the ovalbumin gene has eight exons and seven introns; the gene for cytochrome b has five exons and four introns (I Figure 14.3). All the introns and the exons are initially transcribed into RNA but, after transcription, the introns are removed by splicing and the exons are joined to yield the mature RNA.

Introns are common in eukaryotic genes but are rare in bacterial genes. For a number of years after their discovery,

Question: Is the coding sequence in a gene always continuous?

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