Question

Tallness (T) is dominant to dwarfness (t), while red (R) flower color is dominant to white (r). The heterozygous condition results in pink (Rr) flower color. A dwarf, red snapdragon is crossed with a plant homozygous for tallness and white flowers. What are the genotype and phenotype of the F1 individuals?

• A. ttRr - dwarf and pink
• B. ttrr - dwarf and white
• C. TtRr - tall and red
• D. TtRr - tall and pink

Hint:

Incomplete dominance in snapdragons (*Antirrhinum majus*) is a classic genetic example where heterozygotes ($Rr$) show an intermediate pink phenotype instead of the dominant red color.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
This problem analyzes the inheritance of two traits: plant height (which exhibits complete dominance) and flower color (which exhibits incomplete dominance).

Step 2: Detailed Explanation:
- Determine the genotypes of the parent plants:
1. Dwarf, red snapdragon: Dwarf is recessive ($tt$), and red is dominant ($RR$).
Genotype = $ttRR$.
2. Homozygous tall, white snapdragon: Tall is dominant ($TT$), and white is recessive ($rr$).
Genotype = $TTrr$.
- Set up the cross:
\[ ttRR \times TTrr \] - The gametes produced are:
- Parent 1 ($ttRR$) produces $tR$ gametes.
- Parent 2 ($TTrr$) produces $Tr$ gametes.
- Combine these gametes to determine the $\text{F}_1$ genotype:
\[ tR \times Tr \longrightarrow TtRr \] - Determine the $\text{F}_1$ phenotype:
- The $Tt$ genotype produces a tall phenotype because tallness ($T$) is completely dominant to dwarfness ($t$).
- The $Rr$ genotype produces a pink phenotype due to incomplete dominance between the red ($R$) and white ($r$) alleles.
Therefore, the $\text{F}_1$ individuals are genetically $TtRr$ and phenotypically tall and pink.

Step 3: Final Answer:
The genotype and phenotype of the $\text{F}_1$ individuals are $TtRr$, tall and pink.