Method for preparing a counter-tagged population of nucleic acid molecules
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 of sequencing, comprising:
a) amplifying a population of distinct initial target DNA molecules from a tagged genomic sample thereby producing a population of amplified target DNA molecules, wherein the distinct initial target DNA molecules that comprise a polymorphic target sequence are tagged with: (i) different degenerate base region (DBR) sequences, wherein said DBR sequences comprise at least one nucleotide base selected from: R, Y, S, W, K, M, B, D, H, V, N and modified versions thereof and (ii) a unique multiplex identifier (MID) sequence that identifies a source for each of the initial target DNA molecules to which it is associated, and wherein each of a plurality of the amplified target DNA molecules comprises said polymorphic target sequence, an associated DBR sequence of said different DBR sequences and said unique MID sequence; and
b) sequencing the plurality of the amplified target DNA molecules, thereby producing a plurality of sequence reads, wherein the sequencing step provides, for each of the amplified target DNA molecules that are sequenced: the nucleotide sequence of: (i) at least a portion of the polymorphic target sequence; (ii) an associated DBR sequence of said DBR sequences; and (iii) said unique MID sequence.
2. The method of claim 1 , further comprising:
c) assessing the presence of an allele of said polymorphic target sequence region in said tagged genomic sample based on:
(i) a determination of the number of said different DBR sequences that are associated with said allele;
(ii) a determination of the number of said sequence reads that comprise each of the different DBR sequences that are associated with said allele.
3. The method of claim 2 , wherein the assessing step is done by a computer that is programmed to perform the assessing step.
4. The method of claim 2 , wherein:
the assessing step further comprises independently assessing the presence of an additional allele of the polymorphic target sequence in said tagged genomic sample based on:
(i) a determination of the number of said different DBR sequences that are associated with the additional allele of said polymorphic target sequence; and
(ii) a determination of the number of said sequence reads that comprise each of the different DBR sequences that are associated with the additional allele.
5. The method of claim 2 , wherein the assessing step comprises performing a maximum likelihood analysis.
6. The method of claim 2 , wherein the method further comprises determining the amount of the allele in the tagged genomic sample.
7. The method of claim 1 , wherein said population of distinct initial target DNA molecules is made by ligating a set of adaptors that comprise said DBR sequences to an initial nucleic acid sample.
8. The method of claim 7 , wherein said initial nucleic acid sample is an amplification product.
9. The method of claim 1 , wherein said population of distinct initial target DNA molecules is made by extension of a set of primers that comprises said DBR sequences, using an initial nucleic acid sample as a template.
10. The method of claim 9 , wherein said initial nucleic acid sample is an amplification product.
11. The method of claim 1 , wherein the method comprises, prior to the amplifying step (a), enriching said population of distinct initial target DNA molecules from an initial nucleic acid sample.
12. The method of claim 1 , wherein said DBR sequences comprise 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.
13. The method of claim 12 , wherein the DBR sequences comprise 10 or more nucleotide bases, wherein each of the 10 or more nucleotide bases is selected from: R, Y, S, W, K, M, B, D, H, V, N, and modified versions thereof.
14. The method of claim 12 , wherein the DBR sequences comprise from 3 to 10 nucleotide bases, wherein each of the 3 to 10 nucleotide bases is selected from: R, Y, S, W, M, B, D, H, V, N, and modified versions thereof.
15. The method of claim 1 , wherein the DBR sequences comprise an error correcting code.
16. The method of claim 1 , wherein said tagged genomic sample is a pooled sample comprising nucleic acid molecules from several different sources, where each of said sources is associated with a different MID sequence.
17. The method of claim 16 , wherein each of the sources is derived from a human subject.
18. The method of claim 16 , wherein each of the sources is derived from different sections of a tumor.
19. The method of claim 16 , wherein each of the sources is derived from different tumors of a subject.
20. The method of claim 6 , wherein each of the sources is derived from a subject at different times.
21. The method of claim 1 , wherein the tagged genomic sample comprises polynucleotides from a tumor.
22. The method of claim 1 , wherein the tagged genomic sample comprises polynucleotides from a microorganism and/or a virus.
23. The method of claim 1 , wherein the tagged genomic sample comprises human genomic DNA and said polymorphic target sequence comprises a single nucleotide polymorphism of the human genome.
24. The method of claim 1 , wherein the sequencing step b) comprises sequencing said plurality of amplified target DNA molecules on a next-generation sequencing platform.
25. The method of claim 1 , wherein the amplifying step is done by polymerase chain reaction.