Increasing confidence of allele calls with molecular counting
Aspects of the present invention include methods and compositions for determining the number of individual polynucleotide molecules originating from the same genomic region of the same original sample that have been sequenced in a particular sequence analysis configuration or process. In these aspects of the invention, a degenerate base region (DBR) is attached to the starting polynucleotide molecules that are subsequently sequenced (e.g., after certain process steps are performed, e.g., amplification and/or enrichment). The number of different DBR sequences present in a sequencing run can be used to determine/estimate the number of different starting polynucleotides that have been sequenced. DBRs can be used to enhance numerous different nucleic acid sequence analysis applications, including allowing higher confidence allele call determinations in genotyping applications.
1. A method for enhancing a determination of the presence of alleles in a genomic sample, said method comprising:
a) attaching a set of oligonucleotides that comprises a degenerate base region (DBR) comprising at least one nucleotide base selected from: R, Y, S, W, K, M, B, D, H, V, N and modified versions thereof to the nucleic acid molecules of a genomic sample that contains a polymorphic target region, thereby producing a population of adapter-attached polynucleotides in which each of said adaptor-attached polynucleotides that comprises said polymorphic target region is attached to a DBR sequence of an oligonucleotide of said set of oligonucleotides, wherein said oligonucleotides further comprise a unique multiplex identifier (MID) sequence that identifies a source for each of the nucleic acid molecules to which it is attached;
b) amplifying the adapter-attached polynucleotides, thereby producing amplified adapter-attached polynucleotides that contain the polymorphic target region;
c) sequencing some of the amplified adapter-attached polynucleotides that contain the polymorphic target region, thereby producing a plurality of sequences, wherein the sequencing step provides, for each of the amplified adaptor-attached polynucleotides that contain the polymorphic target region and are sequenced: (i) the nucleotide sequence of at least a portion of said polymorphic target region and (ii) the DBR sequence of the oligonucleotide to which said polymorphic target region is attached;
d) determining, for one allele of the polymorphic target region, the number of different DBR sequences in the oligonucleotides that are associated with said allele; and
e) repeating step d) for additional alleles of said polymorphic target region, thereby enhancing said determination of the presence of said alleles in said genomic sample based on the numbers of different DBR sequences in the oligonucleotides that are associated with said allele and said additional alleles.
2. The method of claim 1 , further comprising:
f) independently calculating the likelihood that each of the alleles is present in said genomic sample using the numbers of different DBR sequences in the oligonucleotides that are associated with said allele and said additional alleles; and
g) calling a genotype for said genomic sample based on the likelihood calculated in step f).
3. The method of claim 1 , wherein said oligonucleotides comprise a degenerate base region comprises at least 2 nucleotide bases, wherein each of the at least 2 nucleotide bases are selected from: R, Y, S, W, K, M, B, D, H, V, N, and modified versions thereof.
4. The method of claim 3 , wherein the degenerate base region comprises from 3 to 20 nucleotide bases, wherein each of the 3 to 10 nucleotide bases is selected from: R, Y, S, W, K, M, B, D, H, V, N, and modified versions thereof.
5. The method of claim 1 , wherein the oligonucleotides further comprises a sequencing primer site.
6. The method of claim 1 , wherein said method further comprises combining said population of adapter-attached polynucleotides with other populations of adaptor attached polynucleotides, and wherein each of said populations of adaptor attached polynucleotides is associated with said unique MID sequence.
7. The method of claim 1 , wherein said sequencing step comprises sequencing said some of the amplified adapter-attached polynucleotides on a next-generation sequencing platform.
8. The method of claim 1 , wherein the genomic sample containing said polymorphic target region is enriched prior to the attaching step.
9. The method of claim 1 , wherein the genomic sample containing said polymorphic target region is enriched prior to the sequencing step.
10. The method of claim 1 , wherein the genomic sample comprises polynucleotides made from a tumor tissue.
11. The method of claim 1 , wherein the genomic sample comprises polynucleotides made from microorganisms and/or viruses.
12. The method of claim 1 , wherein said attaching step comprises ligating said set of oligonucleotides to the nucleic acid molecules of said genomic sample.
13. The method of claim 1 , wherein said set of oligonucleotides are primers and the attaching step is done by primer extension.
14. The method of claim 1 , wherein said genomic sample comprises multiple genomic samples derived from different sources.
15. The method of claim 14 , wherein each of the multiple genomic samples is derived from a different subject.
16. The method of claim 14 , wherein each of the multiple genomic samples is derived from a different human subject.
17. The method of claim 14 , wherein the multiple genomic samples are derived from different sections of a tumor.
18. The method of claim 14 , wherein the multiple genomic samples are derived from different tumors from a subject.
19. The method of claim 14 , wherein the multiple genomic samples are derived from a subject over time.
20. The method of claim 19 , wherein the polymorphic target region is in a viral sample.