You Are Using Phages to Map Three Toxin-Production Genes (R

question 41

Short Answer

You are using phages to map three toxin-production genes (R, Y, and
G) in a new bacterium. You grow phages in a strain of the bacteria that produces all three toxins (R⁺, Y⁺, G⁺), isolate the phage, and then infect a second bacterial strain that cannot produce any of the toxins (R^-, Y^-, G^-). The recipient bacteria are then grown on colorimetric media (media that change color in response to toxin presence) to see which toxin genes are transferred together by the phage. The data are as follows:
$$\begin{array} { l l l l } & \mathrm { R } & \mathrm { Y } & \mathrm { G } \\\mathrm { R } & - & 76 \% & 0 \% \\\mathrm { Y } & & - & 3 \% \\\mathrm { G } & & & -\end{array}$$
a. What kind of mapping is this called?
b. Which gene is in the middle?
c. Which of the outside genes is closer to the middle gene?

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