A homozygous tall pea plant with yellow pods is crossed with a homozygous dwarf pea plant with the green pods. The off springs produced are salted. In the `F_2` generation , the ratio of plants having parental combinations to new combinations is

Options

A. `10:6`
B. `6:10`
C. `9:7`
D. `7:9`

Answer

To solve the problem of determining the ratio of parental combinations to new combinations in the F2 generation of pea plants, we will follow these steps:

### Step 1: Identify the Traits and Genotypes of the Parents
- We have two traits: height (tall vs. dwarf) and pod color (yellow vs. green).
- Tall (T) is dominant over dwarf (t), and yellow (G) is dominant over green (g).
- The genotypes of the parents are:
- Homozygous tall with yellow pods: **TTGG**
- Homozygous dwarf with green pods: **ttgg**

### Step 2: Determine the F1 Generation
- When we cross the two parents (TTGG x ttgg), all offspring in the F1 generation will be heterozygous for both traits.
- The genotype of the F1 generation will be: **TtGg** (tall with yellow pods).

### Step 3: Self-Cross the F1 Generation
- The F1 plants (TtGg) will be self-crossed to produce the F2 generation.
- The possible gametes from TtGg are: **TG, Tg, tG, tg**.

### Step 4: Create a Punnett Square for the F2 Generation
- We will set up a 4x4 Punnett square to find all combinations of the gametes:

| | TG | Tg | tG | tg |
|-------|------|------|------|------|
| **TG** | TTGG | TTGg | TtGG | TtGg |
| **Tg** | TTGg | TTgg | TtGg | Ttgg |
| **tG** | TtGG | TtGg | ttGG | ttGg |
| **tg** | TtGg | Ttgg | ttGg | ttgg |

### Step 5: Determine the Phenotypes from the Genotypes
- Now we will classify the phenotypes based on the genotypes:
- **Tall with yellow pods (TY)**: TTGG, TTGg, TtGG, TtGg (6 total)
- **Tall with green pods (TG)**: TtGg, Ttgg (2 total)
- **Dwarf with yellow pods (DY)**: ttGg (2 total)
- **Dwarf with green pods (DG)**: ttgg (1 total)

### Step 6: Count Parental and Recombinant Combinations
- **Parental combinations**:
- Tall yellow (TY): 6
- Dwarf green (DG): 1
- Total parental combinations = 6 + 1 = 7

- **New combinations (recombinants)**:
- Tall green (TG): 2
- Dwarf yellow (DY): 2
- Total new combinations = 2 + 2 = 4

### Step 7: Calculate the Ratio
- The ratio of parental combinations to new combinations is:
- Parental combinations: 7
- New combinations: 4
- Therefore, the ratio is **7:4**.

### Final Answer
The ratio of plants having parental combinations to new combinations in the F2 generation is **7:4**.

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