3. In a transformation experiment involving a recipient bacterial strain of genotype a- b- the results below were obtained. What can you conclude about the location of the a and b genes relative to each other? (hint: are they close together or far apart?)
Consider this as two separate experiments. In the first experiment, a DNA strand containing a+ b+ genes were placed in a culture of bacteria with a- b- genes. In this experiment there is only one DNA strand, so only one transformation event can occur. However, three things could happen: only the a gene could be transformed, only the b gene could be transformed or both a and b genes could be transformed. In other words the recipient DNA could take up only the a gene, only the b gene or the entire a+ b+ strand. The a+ b+ transformants % shows you the percentage of transformants where the entire a+ b+ was incorporated into the a- b- bacteria.
In the second experiment, there are two DNA strands added to the original a- b- culture. So, there can be three different transforming events. The a- b- can be transformed by the a+ b- strand; by the a- b+ strand or by both. The a+ b+ transformants % shows you the percentage of transformants where the two separate and independent events occurred resulting in a- b- bacteria being transformed into a+ b+ bacteria.
How does the information from both experiments help you determine the location of the a and be genes relative to each other?
Transformants (%)
Transforming DNA a+ b- a- b+ a+ b+
a+ b+ 3.1 1.2 0.04
a+ b- and a- b+ 2.4 1.4 0.03