Differentiation is the process by which unspecialised cells become specialised for a particular function, for example a red blood cell, neurone or palisade cell.Almost every cell in an organism contains the same genes, because all cells come from the zygote by mitosis. Cells become different because they use different genes. This is differential gene expression: in each cell type some genes are switched on and others are switched off. Genes are switched on or off by proteins called transcription factors, which bind to DNA and control whether a gene is transcribed into mRNA. Only active genes produce mRNA, which is translated into proteins, and these proteins change the structure and function of the cell. For example, a developing red blood cell makes large amounts of haemoglobin and loses its nucleus.Unspecialised cells that can divide and differentiate are called stem cells:
• totipotent cells can give rise to any cell type, including the cells of the placenta. The zygote and the cells of the early embryo up to about the 16-cell stage are totipotent.
• pluripotent cells, such as those of the inner cell mass of the blastocyst, can form any body cell but not the placenta.
• multipotent cells, such as adult stem cells in bone marrow, can only form a few cell types, such as blood cells.As cells differentiate they usually lose the ability to become other cell types. In plants, stem cells are found in meristems.
• totipotent cells can give rise to any cell type, including the cells of the placenta. The zygote and the cells of the early embryo up to about the 16-cell stage are totipotent.
• pluripotent cells, such as those of the inner cell mass of the blastocyst, can form any body cell but not the placenta.
• multipotent cells, such as adult stem cells in bone marrow, can only form a few cell types, such as blood cells.As cells differentiate they usually lose the ability to become other cell types. In plants, stem cells are found in meristems.