Step 2 - Measuring The Observations
The second chi-square step is where the researchers go out to the field or greenhouse to count the number of F2 tomato plants which were resistant and those which were susceptible. This is known as “phenotyping” (Fig. 4). In this particular case, they found 141 resistant F2 tomato plants and 56 susceptible.
Figure 4. Example of phenotyping, with a plot that includes plants that are resistant (left) and susceptible (mid-right) to bacterial spot.
In “genotyping” the researchers will look at various DNA marker patterns for each of the F2 plants. Rather than scoring plants or categorizing them based upon their phenotype (resistant or susceptible to bacterial spot), the plants are scored based upon patterns seen for a DNA marker. If you want, you can skip ahead in this less to follow an example of genotyping.