Which of the following statement for chromosomal theory of inheritance is incorrect ?

Options

A. Pairing and segregation of a pair of chromosomes would lead to the segregation of a factor they carried
B. Behaviour of chromosomes is parallel to the behaviour of genes
C. The two alleles of a gene pair are located on homologous sites on homologous chromosomes
D. Chromosomes as well as genes occur in pairs

Answer

To determine which statement regarding the chromosomal theory of inheritance is incorrect, we can analyze the options given. Here’s a step-by-step solution:

### Step 1: Understand the Chromosomal Theory of Inheritance
The chromosomal theory of inheritance states that genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization is responsible for the inheritance of traits.

### Step 2: Analyze Each Statement
1. **Statement 1**: "Pairing and segregation of a pair of chromosomes would lead to the segregation of a factor they carry."
- **Analysis**: The term "segregation" is used incorrectly here. It should refer to "separation" of chromosomes during meiosis, which leads to the segregation of alleles (factors). Thus, this statement is incorrect.

2. **Statement 2**: "The behavior of chromosomes is parallel to the behavior of genes."
- **Analysis**: This statement is true. The behavior of chromosomes during cell division reflects the behavior of genes.

3. **Statement 3**: "Chromosomes as well as genes occur in pairs."
- **Analysis**: This statement is also true. Chromosomes exist in homologous pairs, and genes are present in pairs (alleles).

4. **Statement 4**: "The two alleles of a gene pair are located on the homologous site on the homologous chromosome."
- **Analysis**: This statement is true. Alleles for a gene are found at the same locus on homologous chromosomes.

### Step 3: Identify the Incorrect Statement
From the analysis, the first statement is identified as incorrect because it misuses the term "segregation" instead of "separation."

### Final Answer
The incorrect statement regarding the chromosomal theory of inheritance is:
**"Pairing and segregation of a pair of chromosomes would lead to the segregation of a factor they carry."**

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