US9708642

Method and system for DNA mixture analysis

The present invention pertains to a process for automatically analyzing mixed DNA samples. Specifically, the process comprises the steps of obtaining a mixed DNA sample; amplifying the DNA sample to produce a product; detecting the product to produce a signal; and analyzing the signal to determine information about the composition of the mixed DNA sample. This DNA mixture analysis is useful for finding criminals and convicting them. This mixture analysis provides high quality estimates, and can determine genotypes, mixture weights, and likelihood ratios. This analysis provides confidence measures in the results it computes, and generates reports and intuitive visualizations. The process automates a tedious manual procedure, thereby reducing the cost, time, and effort involved in DNA forensic analysis. The system can greatly accelerate the rate of DNA crime analysis, and be used to exonerate innocent people.

1. A method of analyzing a biological sample comprised of the steps:
   1. obtaining a biological sample that contains DNA;
   2. amplifying the DNA to produce a product;
   3. detecting the product to generate data, where the data can be explained by more than one genotype value;
   4. assuming a genotype value which is stored in a nontransient memory;
   5. deriving with a computer a variance of the amplification; and
   6. determining a likelihood using a computer in communication with the memory, where the likelihood is defined as a probability of observing the generated data, and said probability depends on the genotype value and the variance.
2. A method as described in claim 1 where after the likelihood determining step there is the step of calculating a likelihood ratio of a hypothesis using the determined likelihood.
3. A method as described in claim 2 where the hypothesis involves an individual contributing their DNA to the biological sample.
4. A method as described in claim 3 where the hypothesis is related to an identity of the individual.
5. A method as described in claim 4 where the likelihood ratio is calculated for two different hypotheses.
6. A method as described in claim 5 where the biological sample is a mixture of DNA from two or more individuals.
7. A method as described in claim 6 where after the genotype assuming step there is the step of forming a linear combination of the genotype values.
8. A method as described in claim 7 where after the product detecting step there is the step of setting a quantity value related to how much DNA an individual contributed to the mixture.
9. A method as described in claim 8 where the linear combination of genotype values is weighted by the quantity values.
10. A method as described in claim 9 where the data relates to a short tandem repeat (STR) genetic locus.
11. A method as described in claim 10 where the data contains polymerase chain reaction (PCR) stutter.
12. A method as described in claim 11 where the determined likelihood includes as a conditional parameter a number of contributors to the biological sample.
13. A method as described in claim 12 where the amplification step is repeated to obtain additional data for determining the likelihood.
14. A method as described in claim 13 where the likelihood is used in making a comparison with a DNA database.
15. A method as described in claim 14, where the likelihood in Step (f) is determined using a Markov chain Monte Carlo method.
16. A method as described in claim 15, where the data variance value in Step (e) is derived using a calibration.