Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:(1995) found a mosaic pattern of staining of neurons, including Purkinje cells, from a MERRF patient who exhibited a moderate proportion of mutant DNA in brain (55% in brain total DNA and 59% in brain mitochondrial DNA; Lombes et al., 1992) when they used antisera directed against cytochrome c oxidase subunit II. The data that we have obtained in the present work on the Purkinje cell pairs would suggest that, among those cells, the level of mutant mtDNA varied very little from cell to cell. Thus, the mosaic phenotype observed by Sparaco et al. (1995) may have arisen from a failure of the residual wild-type DNA to complement the mutant DNA in some cells because of an unfavorable segregation of the two genotypes within the cells.
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