Imagine that you are interested in determining the relative order of three genes
ID: 58602 • Letter: I
Question
Imagine that you are interested in determining the relative order of three genes (x, y, and z) on a bacterial chromosome. You fragment a DNA sample from this species of bacteria and use the resulting fragments to transform a bacterial strain that has non-functional mutant copies of these three genes. By screening the phenotypes of the transformants, you determine the frequency with which each of the following pairs of genes were co- transformed.
Gene Pair Co-Transformation Frequency
x-y 90%
x-z 80%
y-z 65%
What is the order of the three genes on the chromosome? Briefly explain the logic you used to reach this conclusion.
Explanation / Answer
Co-transformation of a gene pair is possible when two genes appear closer to each other on the same chromosome.
Since X-Y co transformed 90% they both are more close to each other, the next highest cotransformed gene pair is X-Z. therefore the order of the three genes on the chromosome will be
Y--------X--------Z---
90% 80%