Chapter 18, Problem 9P

Figure 18.6 shows a picture of Glofish ^®, transgenic zebrafish (Danio rerio) that express GFP, RFP, and some of their derivatives. Glofish^® were the first GM pets. Genes can be transferred into the zebrafish genome using a transposable element called Tol2 from medaka fish (Oryzias latipes). The Tol2 transposon serves as a vector for gene transfer in a manner similar to Drosophila P elements as shown in Fig. 18.4. To use the Tol2 vector, researchers inject two-cell stage zebrafish embryos with two DNAs: One DNA expresses the Tol2 transposase gene, while the other recombinant transposon contains the transgene. If the transposon hops into a chromosome of a germ-line cell, a stable line of transgenic fish can be established.

Scientists have synthesized several different genes encoding derivatives of GFP and RFP. The derivatives have amino acid changes that alter their color, so that fish glowing green, red, orange, blue, or purple are available in many pet stores.

a.	Diagram the two recombinant DNA constructs needed to generate the fluorescent fish.
b	Why is a transposon from medaka fish used rather than a zebrafish transposon?