Explanation:
We are given a genetics problem about
incomplete dominance in snapdragon flowers.
Key facts from the problem:
- Red flower color (R) is incompletely dominant over white (r).
- That means:
- RR = red
- rr = white
- Rr = pink (a blend — the “incomplete” part)
So:
- Red plant genotype =
RR
- White plant genotype =
rr
- Pink plant genotype =
Rr
Now let’s solve each cross:
---
A. A pink flowered plant crossed with a red one.
Pink = Rr
Red = RR
Punnett Square:
| | R | R |
|-------|------|------|
|
R | RR | RR |
|
r | Rr | Rr |
Genotypes:
- 2 RR
- 2 Rr
Phenotypes:
- RR = red
- Rr = pink
→ So:
2 red, 2 pink
Phenotypic ratio =
1 : 1 (red : pink)
---
B. A pink flowered plant crossed with a white one.
Pink = Rr
White = rr
Punnett Square:
| | r | r |
|-------|------|------|
|
R | Rr | Rr |
|
r | rr | rr |
Genotypes:
- 2 Rr
- 2 rr
Phenotypes:
- Rr = pink
- rr = white
→ So:
2 pink, 2 white
Phenotypic ratio =
1 : 1 (pink : white)
---
C. A pink flowered plant crossed with another pink one.
Pink × Pink = Rr × Rr
Punnett Square:
| | R | r |
|-------|------|------|
|
R | RR | Rr |
|
r | Rr | rr |
Genotypes:
- 1 RR
- 2 Rr
- 1 rr
Phenotypes:
- RR = red
- Rr = pink
- rr = white
→ So:
1 red : 2 pink : 1 white
Phenotypic ratio =
1 : 2 : 1
---
Final Answer:
A. Cross: Rr × RR → Phenotypic ratio: 1 red : 1 pink
B. Cross: Rr × rr → Phenotypic ratio: 1 pink : 1 white
C. Cross: Rr × Rr → Phenotypic ratio: 1 red : 2 pink : 1 white
Parent Tip: Review the logic above to help your child master the concept of codominance punnett square worksheet.
