Differentiation Higher Human Biology

Differentiation unspecialised cells become altered and adapted perform a specialised function permanent tissue Division of labour Multicellular organisms

Differentiation in Human Cells Fertilised egg (zygote) Divides rapidly by mitosis and cell division to form an embryo Many different specialised cells created – each adapted to suit its function.

Each embryonic cell contains all the genes for constructing the whole organism Unlike adult cells these genes are either switched on/ have the potential to be switched on.

As embryological development proceeds embryonic cells become differentiated and specialised in; – Structure – Biochemical properties Perfectly adapted to carry out particular functions.

Somatic cells B Lymphocyte Hyaline cartilage Smooth muscle

Somatic cells Ciliated epithelial cell Red blood cell platelets neutrophil

Somatic cells Cardiac muscle Nerve cells Squamous epithelial cells T lymphocyte

Selective Gene Expression Differentiated cells only express the genes that code for the proteins specific to the workings of that particular cell.

Nerve cells - genes that code for formation of neurotransmitter substances switched on - genes for production of mucus switched off. Goblet cells – genes that code for mucus production switched on - Genes that code for neurotransmitters switched off.

Only a fraction of genes in a specialised cell are expressed. Approx 3 – 5 % in a typical human cell.