Animal Development

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   cloning      damaged      eight cell stage      embryo      embryonic stem cells      identical      mitosis      not active      proteins      reactivate      same genes      specialised   
The zygote divides by to form an .

In a human embryo, up to the , all the cells are and could produce any sort of cell required by the organism.

They are called .

After this point the cells become and form different types of tissue.

Although body cells in an organism contain the , many genes in a particular cell are .

This is because it only produces the specific it needs;

In carefully controlled conditions of mammalian , it is possible to inactive genes in the nucleus of a body cell to form cells of all tissue types.

Adult and embryonic stem cells have the potential to produce cells needed to replace tissues.