Streptococcus pneumonia cells of genotype strs mtl- are transformed by donor DNA of genotype strs mt+ and by a mixture of two DNAs with genotypes strs mtl- and strs mt--.
In the given table:
| Percentage of cells transformed | |||
| Transforming DNA | str s mtl - | str s mt + | str s mt + |
| str s mt + | 4.3 | 0.40 | 0.17 |
| str s mtl - str s mt + | 2.8 | 0.85 | 0.0066 |
a. The first row of the table indicates that the two genes are far enough apart to be located on separate DNA fragments. The frequency of double transformants should be the product of the frequency of the two single transformants, or (4.3%) (0.40%) = 0.017%. The observed double transformants frequency is 0.17%, a factor of 10 greater than expected.
Therefore, the two genes are located close enough together to be co-transformed at a rate of 0.17%.
b. The second row of the table indicates that the two genes strr mtl‾ and strs mtl+ must be contained on separate pieces of DNA. Therefore, the percentage of co-transformation is much lower.