The experiment with the crossbreeding can be diagramed in a different manner. Using Y for a dominant trait and G for the recessive trait, we can see why Mendel found a 3:1 ratio of the dominant characteristic to the recessive one. Only when the two recessive traits are paired with each other do they express that characteristic.
In the first generation, the pairing of genetic material from both parents looked something like this:
If parent 1 was a green color and parent 2 a yellow color, the contributions all had to look like one green trait and one yellow trait paired together. What Mendel observed were all yellow colored plants.
During the second generation, Mendel selected plants from the first generation and pollinated these to come out with his second generation. That pairing looked like this if we chart it in the same way as we did for the first generation:
Both parents were yellow in color but one out of four offspring were green. This means that the green had been present in both parents but had not expressed itself physically. In other words, it had been "recessed" behind the "dominant" yellow characteristic.
Gregor Mendel discovered that there was a different between what one physically could see and what was happening "behind the scenes" in a genetic sense. He also could see that there were both Dominant and Recessive elements as a result of this experiment. When paired together, only one of them was expressed (seen). This was the Dominant element and the other the Recessive element - present but unseen. This distinction between Dominant and Recessive traits enables us to define the difference between the pairing of genes and the appearance of something. It is equally clear that when the two different traits are paired together that the recessive or weaker trait is not affected by the dominant trait so that it can be expressed within the next generation. Mendel also proved that each parent contributes genes to offspring.
