Deletion of the promoter and the first exon of the DNA polymerase beta
gene (pol beta) in the mouse germ line results in a lethal phenotype.
With the use of the bacteriophage-derived, site-specific recombinase
Cre in a transgenic approach, the same mutation can be selectively int
roduced into a particular cellular compartment-in this case, T cells.
The impact of the mutation on those cells can then be analyzed because
the mutant animals are viable.