THE ANSWERS
| R | r | |
| r | ||
| r |
As shown in the answers above, there are only two different genotypes:
1) Rr and 2) rr
There are only two phenotypes, to go with the two genotypes:
1) A red stem and 2) A green stem
Since there are only four possibilities in the square. Since there are two ways that the stem would be red, it has a fifty percent chance of being red. There are also two chances of being green, so there is also a fifty percent chance of having a green stem.