Which of the following is not a direct conclusion that can be drawn from Mendel's Experiment?

Options

A. Only one parental trait is expressed
B. Two copies of each trait are inherited in sexually reproducing organism
C. For recessive trait to be expressed, both copies should be identical
D. Natural selection can alter frequency of an inherited trait

Explanation

To determine which of the following is not a direct conclusion that can be drawn from Mendel's experiment, we need to analyze each option based on Mendel's findings regarding inheritance patterns in pea plants.

### Step-by-Step Solution:

1. **Understanding Mendel's Experiment**: Mendel conducted experiments on pea plants (Pisum sativum) to study how traits are inherited. He formulated several key principles based on his observations.

2. **Identifying Mendel's Conclusions**:
- **Law of Dominance**: When contrasting traits are crossed, one trait (dominant) will be expressed in the offspring, while the other (recessive) will not.
- **Law of Segregation**: Each organism carries two alleles for each trait, which segregate during gamete formation, resulting in offspring inheriting one allele from each parent.
- **Law of Independent Assortment**: Genes for different traits are inherited independently of one another.

3. **Evaluating the Options**:
- **Option 1**: "Only one parental trait is expressed" - This aligns with the Law of Dominance.
- **Option 2**: "Two copies of each trait are inherited in sexually reproducing organisms" - This aligns with the Law of Segregation.
- **Option 3**: "For a recessive trait to be expressed, both copies should be identical" - This is also a conclusion from Mendel's work.
- **Option 4**: "Natural selection can alter the frequency of an inherited trait" - This statement is not a conclusion from Mendel's experiments. It pertains to Darwin's theory of natural selection, which is separate from Mendelian genetics.

4. **Conclusion**: The option that is not a direct conclusion from Mendel's experiment is **Option 4: "Natural selection can alter frequency of an inherited trait."**

### Final Answer:
The correct answer is **Option 4**.