Which one of the following is the genotypic ratio in monohybrid cross?

Options

A. `9:3:3:1`
B. `1:2:1`
C. `9:7`
D. `3:1`

Answer

To determine the genotypic ratio in a monohybrid cross, we can follow these steps:

### Step 1: Understand the Monohybrid Cross
A monohybrid cross involves a single trait that is being studied, typically represented by two alleles (dominant and recessive). For example, let's consider a trait for flower color where "T" represents the dominant allele for tall plants and "t" represents the recessive allele for short plants.

### Step 2: Set Up the Parental Generation
In a typical monohybrid cross, we start with two parent plants that are homozygous for the trait. For example:
- Parent 1: TT (homozygous dominant)
- Parent 2: tt (homozygous recessive)

### Step 3: Determine the F1 Generation
When we cross these two parents (TT x tt), all offspring (F1 generation) will inherit one allele from each parent:
- All F1 offspring will be Tt (heterozygous).

### Step 4: Set Up the F1 Cross
Next, we can perform a self-cross of the F1 generation:
- F1: Tt x Tt

### Step 5: Use a Punnett Square
To find the genotypic ratio, we can set up a Punnett square:
```
T | t
-----------------
T | TT | Tt
-----------------
t | Tt | tt
```

### Step 6: Analyze the Punnett Square
From the Punnett square, we can see the following genotypes:
- 1 TT (homozygous dominant)
- 2 Tt (heterozygous)
- 1 tt (homozygous recessive)

### Step 7: Write the Genotypic Ratio
The genotypic ratio can be summarized as:
- 1 TT : 2 Tt : 1 tt

### Conclusion
Thus, the genotypic ratio in a monohybrid cross is **1:2:1**.

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