Though many of the child plants (about 3 out of 4) will have purple flowers, the actual DNA for each purple-flowered plant may not be the same. Scientists use the term phenotype to mean how a plant (or animal or human) looks or behaves and the term genotype to mean the actual alleles, or genes, that the plant (or person) has in its DNA.
| Hybrid Parent Plant 2 | |||
| ALLELES (GENES) |
R | r | |
| Hybrid Parent Plant 1 | R | RR (purple pure-dominant) |
Rr (purple hybrid) |
| r | rR (purple hybrid) |
rr (white pure-recessive) |
|
For example, the phenotype of a white-flowered plant is 'white' because the flower looks white to the human eye. The genotype must be 'rr' because the white flowers are pure-recessive alleles; for a pea plant to have a white flower, it must have two recessive genes (two 'r' alleles).
For a purple-flowered plant, the phenotype shows up as 'purple' because it looks purple in the sunlight. But, the genotype might be 'RR' or 'Rr' (or 'rR') because the purple flowers need only one dominant allele (one 'R' gene) to make the flower purple – even if the other allele is recessive (an 'r' gene). Whether the genotype is pure-dominant ('RR') or hybrid ('Rr' or 'rR') the plant's phenotype is purple.
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