3.18—Differential gene expression and cell specialisation

Cells in one organism usually contain the same genes, but they become specialised because different genes are switched on or off. Active genes are transcribed into mRNA, translated into proteins, and those proteins alter cell structure or processes.

A transcription factor can increase or reduce RNA-polymerase access to a gene. Changing which proteins are produced therefore changes a cell’s properties without changing its entire DNA sequence.

A muscle precursor and a nerve precursor can share the same genome yet express different sets of proteins, giving them different structures and jobs. Environmental signals can alter transcription-factor activity and gene expression.

Differentiation is not caused by cells losing all unused genes. Epigenetic marks can change how DNA is read without changing the base sequence; that differs from a mutation.