Which of the following statements is/are incorrect regarding genes?
(i) They control the transfer of hereditary characteristics (ii) Nucleolus carries all the genes. (iii) They are part of chromosomes.(iv) They are found only in the nucleus.

Explanation

To determine which statements regarding genes are incorrect, let's analyze each statement one by one:

1. **Statement (i): They control the transfer of hereditary characteristics.**
- This statement is **true**. Genes are responsible for the inheritance of traits from parents to offspring. They carry the information that determines various characteristics.

2. **Statement (ii): Nucleolus carries all the genes.**
- This statement is **incorrect**. The nucleolus is a structure within the nucleus that is primarily involved in the production of ribosomes. While the nucleus contains the majority of the cell's genetic material (DNA), it is not accurate to say that the nucleolus carries all the genes.

3. **Statement (iii): They are part of chromosomes.**
- This statement is **true**. Genes are segments of DNA that are located on chromosomes. Chromosomes are structures that organize and package DNA within the nucleus.

4. **Statement (iv): They are found only in the nucleus.**
- This statement is **incorrect**. While genes are primarily found in the nucleus of eukaryotic cells, prokaryotic cells (like bacteria) do not have a nucleus. In prokaryotes, genetic material is found in the cytoplasm in a more dispersed form.

Based on the analysis above, the incorrect statements regarding genes are:
- **Statement (ii)**: Nucleolus carries all the genes.
- **Statement (iv)**: They are found only in the nucleus.

### Final Answer:
The incorrect statements are (ii) and (iv).