| blastocyst: | a hollow ball of 50 to 100 cells reached after about five days' embryonic development just before implantation in the uterus.
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| cell line: | cells of common descent and type cultured in the laboratory.
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| cell nuclear replacement
| (also called somatic cell nuclear transfer) the procedure of replacing the cell nucleus of an egg with the nucleus from another cell.
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| cell type: | one of over 200 different types of cells in the body, for example blood cells, liver cells, neural cells. Each of these cell types has a different subset of genes switched on ("expressed") and therefore specific characteristics which allow it to serve a specific function in the body.
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| clone: | a cell or organism derived from and genetically identical to another cell or organism.
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| cytoplasm: | a jelly-like substance, which together with the nucleus which it surrounds, forms the cell.
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| dedifferentiation: | the process of inducing a specialised cell to revert towards pluripotency.
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| differentiation: | the process by which less specialised cells develop into more specialised cell types—see Box 1 in Chapter 2.
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| DNA: | deoxyribonucleic acid—the cell's and the body's genetic material.
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| enrichment: | increasing the proportion of stem cells in a tissue sample by removing some of the non-stem cell material.
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| enucleated: | from which the nucleus has been removed (usually of an egg).
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| gamete: | the male sperm or female egg.
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| genome: | the complete genetic material of an individual.
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| in vitro fertilisation: | the fertilisation of an egg by a sperm outside the body.
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| mitochondria: | energy-producing structures in the cytoplasm of a cell.
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| multipotent: | having the capacity to develop into multiple (but not all) cell types.
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| oocyte: | the female egg. |
| plasticity: | the capacity of cells to develop into different cell types.
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| pluripotent: | having the capacity to develop into every cell type in the human body, but not the extra-embryonic tissues such as the placenta and umbilical cord.
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| primitive streak: | a collection of cells which appears at about 14 days after fertilisation from which the central nervous system eventually develops.
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| redifferentiation: | the process of inducing a dedifferentiated cell to differentiate into a (different) specialised cell type.
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| totipotent: | having the capacity to develop into every cell type required for human development, including extra-embryonic tissues.
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| zygote: | the single cell formed when the male sperm fertilises the female egg.
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