Differential gene expression and specialisation

Cell Structure, Reproduction and Development · Stem cells, gene expression and phenotype · note 3 of 6

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Differential gene expression and specialisationSpec 3.18

In short

All the cells of an organism contain the same genes, but each type of cell expresses only some of them. The genes that are expressed are transcribed to give active mRNA, which is translated into specific proteins. These proteins either control cell processes, as enzymes, or determine cell structure, so cells become specialised in animals and in plants.

Every body cell of an organism is produced by mitosis from the zygote, so each contains the same genome. Cells differ because of differential gene expression: in each type of cell, only particular genes are switched on and transcribed to active mRNA. The other genes in that cell are not transcribed.

Particular genes are switched on in a developing cell.
These genes are transcribed to produce mRNA, which is processed into active mRNA.
The mRNA is translated at ribosomes to give specific proteins.
The proteins control cell processes (as enzymes) or determine cell structure, so the cell takes on its particular shape and function.

Animals: in developing red blood cells the haemoglobin genes are expressed, so the cells fill with haemoglobin; in beta cells of the pancreas the insulin gene is expressed; in muscle cells the genes for contractile proteins (actin, myosin) are expressed.
Plants: in cells of the leaf, genes for photosynthetic proteins are expressed, whereas in root hair cells they are not; in xylem cells, genes are expressed for the enzymes that make lignin, which thickens the wall.

This is how a stem cell becomes a specialised cell: a particular set of genes is switched on, and the proteins they code for control the cell's structure and function. It is also why a cell can contain a gene that it never expresses.

Three nuclei with the same genes for haemoglobin, insulin, and actin and myosin: in a red blood cell precursor only the haemoglobin gene is on, in a pancreatic beta cell only the insulin gene, and in a muscle cell only the actin and myosin genes; each active gene is transcribed to mRNA and translated to its protein, giving the specialised cell. — Every cell has the same genes; only some are switched on in each cell type.

Common mistake:

Specialised cells do not lose the other genes. They keep them all but do not transcribe them.

Written and checked against the Edexcel International AS Level Biology (XBI11) specification · Updated October 2026

Frequently asked questions

What is the difference between pluripotent and totipotent stem cells?

Totipotent cells, such as those in the early morula, can become any type of cell including the placenta, so they can form a whole organism. Pluripotent cells, such as the inner cell mass of the blastocyst, can become any body cell but not the extra-embryonic tissues.

How does a cell become specialised?

A cell becomes specialised through differential gene expression. Only some of its genes are transcribed to active mRNA, which is translated into specific proteins. These proteins either control cell processes as enzymes or form part of the cell's structure, so the cell takes on a particular shape and function.

How can one gene code for more than one protein?

After a eukaryotic gene is transcribed to pre-mRNA, introns are removed and exons are joined together. By joining the exons in different combinations (alternative splicing), different mRNAs are made from the same gene and are translated into different proteins.

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