P4: Y-STR haplotype evidence interpretation using discrete Laplace models of the Philippine and Austronesian reference databases
Jae Joseph Russell B. Rodriguez1,2,3, Mikkel Meyer Andersen4,5, Maria Corazon A. De Ungria1,6
1. DNA Analysis Laboratory, Natural Sciences Research Institute, College of Science, University of the Philippines Diliman, Quezon City, Philippines
2. Genetic and Molecular Biology Division, Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños, Laguna, Philippines
3. Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
4. Department of Mathematical Sciences, Aalborg University, Aalborg, Denmark
5. Section of Forensic Genetics, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
6. Program on Biodiversity, Ethnicity, and Forensics, Philippine Genome Center, University of the Philippines, Quezon City, Philippines
Description & Aims
Y-chromosome short tandem repeats (Y-STRs) are important tools in forensic DNA investigations, particularly in isolating a male profile from a male-female mixture such as in a sexual assault case [1- 2]. Estimating the frequency of a Y-STR haplotype, however, is not as straightforward as counting its frequency in the reference database, as the database is a rather small sample of all haplotypes presented in the population. This is further complicated by the fact that uniparental haplotypes are inherited from ancestral haplotypes and are related to one another. Various methods have been developed to estimate Y-STR haplotype frequencies (reviewed in ). One such method is the discrete Laplace model which calculates the frequency in the population taken as a collection of haplotype subgroups derived from an ancestral haplotype [4,5]. The application of the discrete Laplace method had also been extended to mixtures , which is especially relevant in sexual assault cases, where there are multiple assailants or when the victim is male. We previously proposed for the adoption of the discrete Laplace model in interpreting Y-STR DNA matches in the Philippines consistent with the recommendations by the ISFG . However, to provide background in formulating specific guidelines applicable to the national setting, the model has to be tested on actual Philippine haplotypes. One such guideline may pertain to the choice of the reference database to fit the model. The ISFG recommends the use of metapopulations (human populations that share genetic ancestry commonly associated with language groups) as opposed to national databases, which are often defined by political jurisdictions . We conjecture however that the use of the Philippine database may be sufficient. For decades, modern-day political boundaries have largely restricted movements in the vast area of Southeast Asia and the Pacific where populations of Austronesian speakers are spread. Moreover, routine casework is much faster and straightforward if Philippine forensic DNA laboratories use a national database, rather than having to access haplotype databases maintained in many different jurisdictions. We therefore would like to test this proposition by comparing the utility of the two datasets (Philippine vs. Austronesian) while considering different marker combinations that reflect variability in multiplex systems used and the quality of evidence recovered from crime scenes.
We are specifically interested in answering the following questions:
- How do Y-STR haplotype frequency estimates vary when the discrete Laplace model is fitted to the Philippine database in contrast to the Austronesian metapopulation?
- What is the effect of including the known profile/s in the database before fitting the model?
- What is the effect of the number of loci on the likelihood ratios (LRs) calculated for single haplotype matches? for two-person mixtures?
- What is the effect of the number of loci on predicting the contributing haplotypes in mixture deconvolution?
To answer these questions, we propose to fit discrete Laplace models on the both the Austronesian dataset and the Philippine dataset in the Y-chromosome Haplotype Reference Database (YHRD) (https://yhrd.org, Release 67-2022/Feb/07) . Likelihood ratios will be calculated on single haplotypes and two-person mixtures randomly drawn from the Philippine database. Lastly, as an exercise in reporting LR results, simulated casework analysis will be performed on haplotype profiles generated in . For further reading see [11-16]. Our observations will form the basis of recommendations on the interpretation of Y-chromosomal STR evidence for forensic DNA laboratories in the Philippines.
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Date of objection
Expired at November, 14th, 2022