Which statement is not correct

Options

A. Histones rich in arginine are `H_(3)` and `H_(4)`
B. Nucleolar organiser is found in the secondary constriction of a chromosome
C. Polytene chromosomes are found in chironomus
D. B-chromosomes are genetically active.

Answer

To determine which statement is not correct, we will analyze each of the four statements provided in the question.

### Step-by-Step Solution:

1. **Statement 1: Histone rich in arginine are called H3 and H4.**
- Histones are proteins that help package DNA into structural units called nucleosomes. H3 and H4 are indeed histones that are rich in arginine. Therefore, this statement is **correct**.

2. **Statement 2: Nuclear organizers are found in the secondary construction of a chromosome.**
- Nuclear organizers are regions of the chromosome that are associated with the formation of the nucleolus. They are indeed found in the secondary constriction of chromosomes, which is where satellite DNA is located. Thus, this statement is also **correct**.

3. **Statement 3: Polytine chromosomes are found in Chironomus.**
- Polytine chromosomes are large chromosomes that have undergone multiple rounds of replication without cell division, and they are indeed found in the salivary glands of Chironomus midges. Therefore, this statement is **correct**.

4. **Statement 4: Beta chromosomes are genetically active.**
- Beta chromosomes are known to be genetically inert, meaning they do not carry any genes and are not involved in gene expression. Therefore, the statement that beta chromosomes are genetically active is **not correct**.

### Conclusion:
The statement that is not correct is: **"Beta chromosomes are genetically active."**

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