METHODS AND SYSTEMS FOR IDENTIFYING CONTAMINATION IN SAMPLES
Methods and systems for determining if a sample has been contaminated with other genetic material, for example, from another sample in a parallel workflow. The methods and systems compare measured allele fractions to predetermined distributions of allele fractions in order to calculate a likelihood that the sample has been contaminated.
1 . A method for identifying contamination in a sample, comprising:
obtaining a sample comprising genomic material;
determining a sample allelic frequency at one or more polymorphic loci in the genomic material;
comparing said sample allelic frequency to a reference allelic frequency expected to be present in said sample; and
identifying genomic contamination in said sample if there is a statistically-significant difference between said sample allelic frequency and said reference allelic frequency.
2 . The method of claim 1 , wherein said genomic material is selected from DNA and RNA.
3 . The method of claim 1 , wherein said sample allelic frequency is determined across a plurality of polymporphic loci and said comparing step comprises comparing the sample allelic frequency to a reference allelic frequency across said plurality of polymorphic loci that would be expected in the absence of contamination.
4 . The method of claim 1 , wherein said sample allelic frequency is determined by sequencing nucleic acid comprising said polymorphic loci.
5 . The method of claim 4 , wherein said sequencing comprises next-generation sequencing.
6 . The method of claim 1 , wherein said determining step comprises genotyping.
7 . The method of claim 1 , wherein said determining step comprises comparing ratios of fluorescence intensities.
8 . The method of claim 7 , further comprising contacting said genomic material with fluorescently-labeled hybridization probes.
9 . The method of claim 1 , wherein said comparing step comprises creating a summary statistic based upon said sample allelic frequency and said reference allelic frequency.
10 . The method of claim 9 , wherein the summary statistic is selected from mean z-score, median z-score, and maximum z-score.
11 . The method of claim 1 , wherein said reference allelic frequency expected to be present in said sample is based upon a collection of sequence data known to be substantially free from contamination.
12 . The method of claim 1 , wherein said reference allelic frequency expected to be present in said sample is based upon a biomarker observed in an organism from which the sample originated.
13 . The method of claim 1 , wherein the genomic material is from a mammal.
14 . The method of claim 13 , wherein the genomic material is from a human.