Dominant and recessive
Mendel gave names to the two behaviours he had just seen. They are the two most used words in this chapter, so it is worth reading the definitions slowly.
Dominant characteristic
The characteristic that appears in the F1 generation when two contrasting pure lines are crossed. Tall, for stem height.
Recessive characteristic
The characteristic that is hidden in the F1 generation and reappears in the F2. Dwarf, for stem height.
How you tell which is which
You do not decide by looking at one plant. You decide from the result of the cross:
- Whichever form shows in the whole F1 is the dominant one.
- Whichever form vanishes and comes back in the F2, as the smaller group, is the recessive one.
Dominant does not mean better or commoner
It means only that the characteristic shows when both forms are present together. A dominant characteristic can be rare and a recessive one can be everywhere — polydactyly is dominant and uncommon, while blue eyes are recessive and ordinary across much of the world. The word is about which one is visible, nothing else.
The two words
Dominant — shows in the F1. Recessive — hidden in the F1, back in the F2. Neither word says anything about how common or how useful the characteristic is.