The mutation is generated by an insertion of the ROSA β-gal gene trap vector (Friedrich and Soriano 1991).
We assume that each passenger mutation is generated from one background mutation rate process and that whether the mutation is non-silent or silent depends on the genetic code.
For example, when wild-type Pol ε misinserts a nucleotide, the major pathway of error avoidance is exonucleolytic proofreading, whereas the mutation is generated if the mismatch is extended (central arrow).
If a mutation had reached high frequency because of its presence in the same genome where a beneficial mutation is generated, both mutations should appear always linked and should have been first detected at the same transfer number.
The rationale of the mutagenesis was that if a mutation is generated that knocks out the expression of a gene responsible for these effects anywhere in the genome, then as a heterozygote, the eye color could be recognized as different from the norm.
Third, instead of assuming separate background mutation rates for non-silent and silent mutations, we assume that each passenger mutation is generated from one background mutation rate process and that whether the mutation is non-silent or silent depends on the genetic code.
