The genotypic ratio an phenotyti ratio of back cross and test cross of a mendelian monohybrid respectively

Options

A. 3:1 and 1:1
B. 1:1 and 1:1
C. 1:3 and 3:1
D. 1:2 and 1:1

Answer

To solve the question regarding the genotypic ratio of back cross and the phenotypic ratio of test cross in a Mendelian monohybrid cross, we can follow these steps:

### Step 1: Understand the Monohybrid Cross
A monohybrid cross involves a single trait with two alleles. For this example, we will use:
- **Tall (T)** as the dominant trait
- **Dwarf (t)** as the recessive trait

### Step 2: Determine the F1 Generation
When we cross two purebred plants:
- Parent 1: TT (homozygous tall)
- Parent 2: tt (homozygous dwarf)

The F1 generation will all be heterozygous (Tt):
- F1 Generation: 100% Tt (tall)

### Step 3: Perform a Test Cross
A test cross involves crossing the F1 hybrid (Tt) with a homozygous recessive (tt):
- Cross: Tt x tt

### Step 4: Determine the Gametes and Offspring from the Test Cross
The gametes from Tt are T and t, and from tt are t and t:
- Possible offspring:
1. Tt (tall)
2. tt (dwarf)

### Step 5: Calculate the Phenotypic Ratio from the Test Cross
The phenotypic ratio of the offspring from the test cross is:
- Tall (Tt): 1
- Dwarf (tt): 1

Thus, the phenotypic ratio is **1:1**.

### Step 6: Perform a Back Cross
A back cross involves crossing the F1 hybrid (Tt) with a homozygous dominant (TT):
- Cross: Tt x TT

### Step 7: Determine the Gametes and Offspring from the Back Cross
The gametes from Tt are T and t, and from TT are T and T:
- Possible offspring:
1. TT (homozygous tall)
2. Tt (heterozygous tall)

### Step 8: Calculate the Genotypic Ratio from the Back Cross
The genotypic ratio of the offspring from the back cross is:
- TT: 1
- Tt: 1

Thus, the genotypic ratio is also **1:1**.

### Final Answer
- **Genotypic ratio of Back Cross:** 1:1
- **Phenotypic ratio of Test Cross:** 1:1