The combinant phenotypic ratio in `F_(2)` obtained from parental cross having genotypes TTRR x ttrr will be

Options

A. `9:3:3:1`
B. `3:1`
C. `1:2:1`
D. `3:3`

Answer

To determine the combinant phenotypic ratio in F2 obtained from the parental cross of genotypes TTRR (homozygous dominant) and ttrr (homozygous recessive), we can follow these steps:

### Step 1: Identify the Parental Genotypes
The parental genotypes are:
- Parent 1: TTRR
- Parent 2: ttrr

### Step 2: Determine the Gametes Produced by Each Parent
- Parent 1 (TTRR) can produce one type of gamete: TR
- Parent 2 (ttrr) can produce one type of gamete: tr

### Step 3: Perform the F1 Generation Cross
When we cross the gametes from both parents:
- F1 Generation: All offspring will have the genotype TtRr (heterozygous for both traits).

### Step 4: Self-Fertilization of F1 Generation
Now, we will self-fertilize the F1 generation (TtRr x TtRr) to produce the F2 generation.

### Step 5: Determine the Gametes for F1 Generation
The F1 generation (TtRr) can produce four types of gametes:
- TR
- Tr
- tR
- tr

### Step 6: Create a Punnett Square
Using a 4x4 Punnett square, we can determine the genotypes of the F2 generation:
```
TR Tr tR tr
-------------------------
TR | TT RR | TT Rr | Tt RR | Tt Rr |
-------------------------
Tr | TT Rr | TT rr | Tt Rr | Tt rr |
-------------------------
tR | Tt RR | Tt Rr | tt RR | tt Rr |
-------------------------
tr | Tt Rr | Tt rr | tt Rr | tt rr |
```

### Step 7: Count the Phenotypes
From the Punnett square, we can count the phenotypes:
- Dominant for both traits (T_R): 9 (TTRR, TTRr, TtRR, TtRr)
- Dominant for the first trait and recessive for the second (T_rr): 3 (TTrr, Ttrr)
- Recessive for the first trait and dominant for the second (ttR_): 3 (ttRR, ttRr)
- Recessive for both traits (ttrr): 1

### Step 8: Write the Phenotypic Ratio
The phenotypic ratio in F2 is:
- 9 (dominant for both) : 3 (dominant for first, recessive for second) : 3 (recessive for first, dominant for second) : 1 (recessive for both)

Thus, the final combinant phenotypic ratio in F2 is **9:3:3:1**.