which of the following statements is not true of two genes that show 50 % recombination frequency ?

Options

A. The genes may be on different chromosomes
B. The genes are tightly linked
C. The genes show independent assortment
D. If the genes are present on the same chromosome, they undergo more than one crossovers in every meiosis.

Explanation

To determine which statement is not true of two genes that show a 50% recombination frequency, we can analyze the implications of this frequency in terms of gene linkage and arrangement.

### Step-by-Step Solution:

1. **Understanding Recombination Frequency**:
- Recombination frequency is a measure of how often two genes are separated during meiosis due to crossing over. A 50% recombination frequency indicates that the genes are assorting independently.

2. **Analyzing Gene Linkage**:
- If two genes show a 50% recombination frequency, it suggests that they are either on different chromosomes or far apart on the same chromosome. This means that they are not tightly linked.

3. **Evaluating the Statements**:
- **Statement 1**: "The genes may be on different chromosomes."
- This is true, as genes on different chromosomes will assort independently.
- **Statement 2**: "The genes are tightly linked."
- This is not true. A 50% recombination frequency indicates that the genes are not tightly linked; they are either far apart on the same chromosome or on different chromosomes.
- **Statement 3**: "The genes show independent assortment."
- This is true, as independent assortment occurs when genes are not linked.
- **Statement 4**: "If the genes are present on the same chromosome, they undergo more than one crossover in every meiosis."
- This is true, as genes that are far apart can undergo multiple crossovers.

4. **Conclusion**:
- The statement that is not true is: "The genes are tightly linked." This is incorrect because a 50% recombination frequency indicates that the genes are either on different chromosomes or far apart on the same chromosome, thus not tightly linked.

### Final Answer:
The statement that is not true is: **"The genes are tightly linked."**