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| Modern Genetic Analysis Chapter 13. Transposable Genetic Elements Ty Elements in Yeast Figure 13-15 shows the structure of one of the Ty elements in yeast: the Ty1 sequence, which is present in approximately 35 copies in the yeast genome. The 330-bp-long termini (terminal sequences), called d (delta) sequences, are present in about 100 copies of the genome. Yeast d sequences, as well as Ty elements as a whole, show significant sequence divergence. The terminal d sequences are present in direct-repeat orientation, in contrast with transposable elements in bacteria, which carry inverted repeat (IR) sequences. However, like prokaryotic transposons, Ty elements generate a repeated sequence of target DNA (in this case, 5 bp) during transposition. In addition, Ty elements cause mutations by insertion into different genes in the yeast chromosome. It is now known that Ty elements transpose through an RNA intermediate (see the section on retroviruses later in this chapter).

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