Question

a cross between two hybrid purple plants ( purple and white )

Answer 1

Do you mean you crossed two “hybrid” purple plants (each showing purple but derived from a purple × white cross, i.e. likely heterozygous)? I’ll give the common genetic interpretations and what to expect.

1) If purple is a simple dominant allele (P) and white is recessive (p), and each purple parent is a heterozygote (Pp):
- Cross: Pp × Pp
- Genotypes: 25% PP, 50% Pp, 25% pp
- Phenotypes: 75% purple, 25% white
(So about 3 purple : 1 white in the offspring.)

2) If the trait shows incomplete dominance (heterozygote has an intermediate color and the original hybrid appears purple as that intermediate):
- Cross: P1P2 × P1P2
- Genotypes: 25% P1P1, 50% P1P2, 25% P2P2
- Phenotypes: 25% one parent color, 50% intermediate (what you called “hybrid purple”), 25% the other parent color

Real-world caveats:
- Flower color is often polygenic or affected by modifiers, so ratios can deviate from simple Mendelian expectations.
- Environmental effects can change pigment expression.

How to tell which model applies:
- Grow a good number of offspring (50–100) and score their colors.
- If you see ~3:1 purple:white, that supports simple dominance with heterozygous parents.
- If you see ~1:2:1 distinct classes (two parental colors and an intermediate), that supports incomplete dominance.
- You can also test a purple plant by crossing it to a known white (homozygous recessive) plant: if any white offspring appear, the purple parent was heterozygous.

If you tell me the species and how the parents were produced (were they known to be heterozygous?), I can give a more specific prediction and experimental plan.