Dr. Specht’s experiments continued but let’s stop here and evaluate his early results by asking a question. How do you explain the three types of rows observed in step #8?
8a: The M3 plants do not express the unique phenotype that was observed in the M2. The simplest explanation is that the unique phenotype was controlled by environmental influences, not by genetic variation in the M2 plant. Therefore the phenotype was not inherited.
8b: The M3 plants all expressed the unique phenotype observed in the M2. The unique trait is inherited. Furthermore, the M2 plant was only able to pass this phenotype on and were therefore truebreeding for the unique trait. The genetic makeup of the M2 parent of these M3 plants must have been homozygous. The key to understanding this term is the prefix “homo” which means same. If the M2 parent was homozygous and self-pollinates we would expect the M3 progeny to be the same. (How could we test this?)
8c: Some of the M3 plants have the unique phenotype of the M2 parent but others express the normal condition of the original true breeding line. The M2 plants that produced these types of rows must be heterozygous. The key to understanding this term is the prefix “hetero” which means different. Heterozygous parents are not true breeding.