Which of the following is incorrect about the chromosomal Theory of Inheritance ?

Options

A. Genes occurs in pair .
B. Pairing and separation of pair of chromosomes lead to the segregation of a factor they carried .
C. Behaviour of chromosomes is parallel to the behaviour of genes .
D. The two alleles of a genes pair are located on same gene locus .

Answer

To determine which statement is incorrect about the chromosomal Theory of Inheritance, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the Chromosomal Theory of Inheritance**:
The chromosomal theory of inheritance states that chromosomes are the carriers of genetic material and that genes are located on chromosomes. This theory explains how traits are passed from parents to offspring through the segregation and independent assortment of chromosomes during meiosis.

2. **Evaluating the First Statement**:
- **Statement**: "Gene occurs in pair."
- **Analysis**: This statement is correct. Genes are found in pairs on homologous chromosomes, which means that for each gene, there are two alleles (one from each parent).

3. **Evaluating the Second Statement**:
- **Statement**: "Pairing and separation of pair chromosomes lead to segregation of a factor they carried."
- **Analysis**: This statement is incorrect. While chromosomes do pair and separate during meiosis, the segregation of genes does not imply that a factor is lost. Instead, independent genes segregate into gametes, and each gamete receives one allele from each gene pair. Therefore, this statement misrepresents the process.

4. **Evaluating the Third Statement**:
- **Statement**: "The behavior of chromosome is parallel to the behavior of gene."
- **Analysis**: This statement is correct. The behavior of chromosomes during cell division reflects the behavior of genes, as genes are located on chromosomes and are inherited according to the same principles.

5. **Evaluating the Fourth Statement**:
- **Statement**: "The two alleles of a gene pair are located on the same gene locus."
- **Analysis**: This statement is also correct. Alleles of a gene are found at the same locus on homologous chromosomes.

### Conclusion:
From the analysis, the incorrect statement regarding the chromosomal Theory of Inheritance is the second statement: "Pairing and separation of pair chromosomes lead to segregation of a factor they carried."

### Final Answer:
The incorrect statement about the chromosomal Theory of Inheritance is: **"Pairing and separation of pair chromosomes lead to segregation of a factor they carried."**

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