The postulate of Mendel that cannot be explained with monohybrid cross

Options

A. Unit factors in pairs
B. Dominance /recessive
C. Segregation of unit factors
D. Independent assortment of unit factors

Answer

### Step-by-Step Solution:

1. **Understanding Monohybrid Cross**:
- A monohybrid cross involves the genetic mixing of two individuals that differ in a single trait. For example, crossing a tall plant (TT) with a dwarf plant (tt) to observe the inheritance of height.

2. **Reviewing Mendel's Postulates**:
- Mendel proposed several postulates regarding inheritance, including:
- Unit factors in pairs
- Dominance and recessiveness
- Segregation of unit factors
- Independent assortment of unit factors

3. **Evaluating Each Option**:
- **Option 1: Unit factors in pairs**:
- This can be explained by a monohybrid cross as it involves the pairing of alleles (e.g., T and t).
- **Option 2: Dominance or recessiveness**:
- This is also explained by monohybrid crosses, as it shows how dominant traits mask recessive traits (e.g., T is dominant over t).
- **Option 3: Segregation of unit factors**:
- This postulate can also be demonstrated through a monohybrid cross, as it shows how alleles segregate during gamete formation.
- **Option 4: Independent assortment of unit factors**:
- This postulate cannot be explained by a monohybrid cross because it requires the examination of two traits simultaneously (e.g., height and seed color), which is beyond the scope of a monohybrid cross that focuses on one trait.

4. **Conclusion**:
- The postulate of Mendel that cannot be explained with a monohybrid cross is the **independent assortment of unit factors**. Therefore, the correct answer is **Option 4**.