What does it mean for a gene to be turned on or off?

What does it mean for a gene to be turned up or down?

A gene being turned on or off means whether that gene is transcribed or not.

A gene being turned up or down is the level at which the gene is being transcribed

Explanation:

The phenomenon described here is called gene expression. The central dogma of biology is DNA - -> RNA - -> Protein. That is, DNA is transcribed to RNA is translated to protein. When this is happening the gene is said to be "turned on", "active" or "expressed".

However, there are 22,000 genes in the human genome, and only a subset of them are being transcribed in a given cell at a given time. That is, only a subset of them are turned on and making their protein at a given time. Therefore, in order to regulate this, certain factors control whether genes are transcribed.

These are called transcription factors, and their presence at a specific gene promoter is required in order for that gene to be transcribed or switched on.

A gene being turned off and on is not a "yes" or "no" type of switch. A gene can be highly active, or only slightly active, or off entirely. For example, if a gene is turned on and highly expressed, but the cell wants to reduce the expression, gene expression can be reduced to a lower level. This is done by reducing the level of transcription, by for example, reducing the amount of transcription factors or using transcription repressors