All the body cells of a person contain the same genes, but only some of these genes are transcribed in each type of cell. The table shows whether four genes are transcribed (✔) or not transcribed (✗) in three types of human cell.
| Gene | Red blood cell precursor | Pancreatic β-cell | Epidermal (skin) cell |
|---|---|---|---|
| Haemoglobin gene | ✔ | ✗ | ✗ |
| Insulin gene | ✗ | ✔ | ✗ |
| Keratin gene | ✗ | ✗ | ✔ |
| Respiratory-enzyme gene | ✔ | ✔ | ✔ |
Using the table, identify the gene that is transcribed in all three types of cell.
[1]
The haemoglobin gene is present in the pancreatic β-cell but is not transcribed. Suggest how transcription of the haemoglobin gene could be prevented in this cell.
[2]
Explain the advantage to the organism of each type of cell transcribing only some of its genes.
[2]