Find the incorrect statement with respect to chromosomal mapping

Options

A. Crossing - over is important in locating genes on chromosome
B. Recombination frequency depends on the distance between the genes
C. Recombination frequency is inversely proportional to the distance between the genes
D. The sequences and the relative distances between various genes are graphically represented in terms of recombination frequencies

Answer

To find the incorrect statement with respect to chromosomal mapping, we can follow these steps:

### Step 1: Understand Chromosomal Mapping
Chromosomal mapping is a technique used to determine the linear arrangement of genes on a chromosome. It is based on the concept of linkage and recombination frequency between genes.

**Hint:** Think about how genes are arranged on chromosomes and the factors that influence their arrangement.

### Step 2: Review Mendel's Laws of Inheritance
According to Mendel's Law of Independent Assortment, genes that are located on different chromosomes assort independently during gamete formation. However, genes that are located close to each other on the same chromosome may not assort independently due to linkage.

**Hint:** Recall Mendel's experiments and how they relate to the inheritance of traits.

### Step 3: Analyze the Dihybrid Cross
In a dihybrid cross, if two genes are far apart on the same chromosome or on different chromosomes, we observe a mix of parental and recombinant offspring. However, if the genes are linked (close together on the same chromosome), we will see more parental combinations and fewer recombinant combinations.

**Hint:** Consider what happens when genes are linked versus when they are unlinked.

### Step 4: Evaluate the Statements
Now, let's evaluate the statements provided:

1. **To locate genes on the chromosome, crossing over is necessary.** - This statement is correct because crossing over allows us to observe the frequency of recombination.

2. **The frequency of recombination depends on the distance between the genes.** - This statement is also correct; as the distance increases, the frequency of recombination tends to increase.

3. **Frequency of recombination is inversely proportional to the distance between the genes.** - This statement is incorrect. The frequency of recombination is directly proportional to the distance between the genes; as the distance increases, the frequency of recombination also increases.

4. **The sequences between the genes and their relative distances can be graphically represented in the form of recombination frequency.** - This statement is correct; we can create a chromosome map based on recombination frequencies.

**Hint:** Identify which statement contradicts the principles of genetics and chromosomal mapping.

### Step 5: Identify the Incorrect Statement
From the analysis, the incorrect statement is: **"Frequency of recombination is inversely proportional to the distance between the genes."** This is incorrect because the relationship is directly proportional.

**Final Answer:** The incorrect statement is: **"Frequency of recombination is inversely proportional to the distance between the genes."**