A selection method for selecting from a population of cells one or more selectable
genetically transformed cells is described. The population of cells comprises selectable
genetically transformed cells and possible non-transformed cells. Each of the selectable
genetically transformed cells comprises a first expressable nucleotide sequence
encoding a first expression product; and optionally a second expressable nucleotide
sequence encoding a second expression product and/or a third expressable nucleotide
sequence encoding a third expression product. A component is utilisable by the
selectable genetically transformed cells by action of the first expressable nucleotide
sequence or the first expression product and optionally by action of the optional
second expressable nucleotide sequence or the optional second expression product
and/or by, action of the optional third expressable nucleotide sequence or the
optional Third expression product. The component can be present in an amount that
is toxic to the non-transformed cells.
