Solutions For An Introduction to Genetic Analysis Chapter 5 Problem 38P

b) The co-transduction frequency, for pur and pdx is calculated, as the percentage of pur⁺ colonies that are also pdx‾ = 100%(10 + 13)/50 = 46%

c) The unselected locus closest to pur is pdx. It is determined based on co-transduction rates.

d) From the co-transduction frequencies, it is known that pdx is closer to pur than nad. Hence, there are two possible gene orders: pur pdx nad or pdx pur nad. Now, consider how a bacterial chromosome that is pur⁺ pdx⁺ nad⁺ might be generated, given the two gene orders: if pdx is in the middle, 4 crossovers are required to get pur⁺ pdx⁺ nad⁺; if pur is in the middle, only 2 crossovers are required.

The results indicate that there are fewer pur⁺ pdx⁺ nad⁺ transductants than any other class, suggesting that this class is “harder” to generate than the others. This implies that pdx is in the middle, and the gene order is pur pdx nad.