Answer:
In order to determine the function of an unknown gene knockout technique is used. PCR based deletion strategy is used for gene knockout in the case of yeast, which is unicellular species and eukaryotic. On the other hand, in the case of a mouse, which is multicellular and eukaryotic, for gene knock out homologous recombination technique is used.
The PCR based strategy is not appropriate for mice genes knockout, as mice are multicellular species and exhibit complex genome. While yeast constitutes some circular plasmids, known as 2 microns plasmids, which allows PCR based mutagenesis.