All seven gave the same answer
Mendel did not run the experiment once. He ran it on seven different characters of the pea plant, and got the same answer every time.
| Character | Dominant form | Recessive form |
|---|---|---|
| Stem height | Tall | Dwarf |
| Flower colour | Purple | White |
| Flower position | Along the stem (axial) | At the tip (terminal) |
| Pod colour | Green | Yellow |
| Pod shape | Inflated | Constricted |
| Seed shape | Round | Wrinkled |
| Seed colour | Yellow | Green |
Table 20.1 — the seven characters Mendel studied.
Seven experiments, one result
For every one of these characters the pattern held: the F1 plants all showed the dominant form, and the F2 came out at three of the dominant form to one of the recessive.
Watch rows 4 and 7
Green is dominant for pod colour, but green is recessive for seed colour. The same colour behaves in opposite ways in two different characters. Dominance belongs to the character being studied, not to the colour itself — a point worth remembering before the exercise at the end of this chapter.
A repeated result is a rule
One 3 : 1 ratio could be chance. Seven of them, in seven unrelated characters of the same plant, means the machinery producing them is general. That is why Mendel could write a law rather than a story about peas.