flymeariver

hi all! i'm a little bit confused regarding the EGF receptor signaling pathway. if there is a suspicion that one component of the pathway controls the expression of a gene but when a null allele of the receptor is used in a transgenic animal (a mosaic animal, if that matters) so that the cells in the clones have no receptor, wouldn't this mean that the signaling pathway is not activated at all in these cells? and if it indeed means that removing the whole pathway has no effects on the expression of this gene, how could components of the pathway downstream of the receptor be suitable candidates for the regulatory function? thanks in advance for any advice!