Monohybrid Cross Experiment Data

The data collected in the monohybrid cross experiment for the disease lesion trait is given below.

Now Dr. Specht’s objective was to explain this data. He needed to formulate a hypothesis that would be supported by the results of the experiment. The best way to devise a hypothesis is to summarize the results of the experiment in simplest terms.

1. All of the F1 plants had the same phenotype, the normal trait.
2. In both the first cross and the reciprocal cross, the mutant phenotype was not apparent in the F1 but it reappeared in the F2. With both traits, the normal phenotype appeared in about ¾ of the F2 and the dwarf or disease lesion mimic trait in ¼ of the F2.
3. F2 plants with the mutant phenotype were all true breeding. F3 progeny of mutant F2s all expressed the mutant trait.
4. Two types of plants had the normal phenotype in the F2. About 1/3 of the F2 normals were true breeding and only produced F3 progeny with the normal phenotype. The other 2/3 of the normal F2s produced both normal and mutant F3 offspring, again in a 3:1 ratio.