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

Options

A. Pairing and saparation of a pair o chromosomes would lead to the segregation of a factor they carried
B. Beheviour of chromosomes is parallel to the behaviour of genes
C. The two alleles of a gene pair one 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 will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Chromosomal Theory of Inheritance**:
- The chromosomal theory of inheritance states that genes are located on chromosomes, and the behavior of chromosomes during meiosis explains the inheritance patterns observed in organisms.

2. **Analyzing Option A**:
- **Statement**: "Pairing and separation of a pair of chromosomes would lead to the segregation of a factor they carried."
- **Analysis**: This statement is incorrect because segregation occurs during the separation of chromosomes, not during pairing. Pairing happens during prophase of meiosis, and it is the separation of homologous chromosomes during anaphase that leads to segregation.

3. **Analyzing Option B**:
- **Statement**: "Behavior of chromosome is parallel to the behavior of gene."
- **Analysis**: This statement is correct. The behavior of chromosomes during meiosis (such as segregation and independent assortment) is indeed parallel to the behavior of genes located on those chromosomes.

4. **Analyzing Option C**:
- **Statement**: "Two alleles of a gene pair, one located on homologous sites on the homologous chromosome."
- **Analysis**: This statement is correct. Each homologous chromosome carries one allele for a given gene at the same locus.

5. **Analyzing Option D**:
- **Statement**: "Chromosomes as well as genes."
- **Analysis**: This statement is also correct. Each homologous chromosome pair contains genes at corresponding loci, which are responsible for the same trait.

6. **Conclusion**:
- After analyzing all the options, we find that the incorrect statement is **Option A**.

### Final Answer:
The incorrect statement regarding the chromosomal theory of inheritance is **Option A**.

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