Mismatch distribution analysis of Y-STR haplotypes as a tool for the evaluation of identity-by-state proportions and significance of matches--the European picture

We suggest the use of the mismatch distribution methodology as an easy way to estimate the distance between all pairs of haplotypes present in a sample. This approach allows the evaluation of the proportion of pairs of Y-STR haplotypes that are prone to become identical by state (IBS), in one generation, by recurrent mutation, a statistic of major importance in the forensic field. The mismatch approach presents some advantages alternatively to the empirical one, since it is not necessary to have simultaneous information on STRs and SNPs, and it allows the evaluation of IBS also within-haplogroups. The estimation of IBS at an European scale showed that there is a high population substructuring for this parameter, increasing from southern-central European countries towards west and north, in accordance to what was found for Y-biallelic markers. This result seems to imply a more careful use of large databases for matching evaluation, even in the absence of population structure for general Y-STR diversity. Furthermore, mismatch distribution can be used to measure the distance between a particular haplotype and all the haplotypes in a sample. When applied to the most frequent haplotypes in Europe it revealed that the opportunity for IBS is not directly related to the frequency of a haplotype, but highly dependent on the proportion of neighbouring haplotypes--so, that reporting on the haplotype frequency for evaluating the significance of a match can be misleading.     

Estimation of postmortem interval in real cases based on experimentally obtained entomological evidence

Using the entomological evidence obtained in several forensic cases analyzed in our laboratory for comparison, we evaluated the results of an experimental study carried out in a semiurban setting to determine the structure of the sarcosaprophagous fauna from a Mediterranean region of SE Spain. In all, 18 orders of arthropods were collected. The summarized experimental results refer to the most important taxa for estimating the postmortem interval. Thus, the seasonal character of certain Diptera species, such as Phaenicia sericata, Calliphora vicina, Chrysomya albiceps and Musca domestica, is cited. Among the Coleoptera, the role of Dermestidae as a necrophagous species, and of Staphylinidae and Histeridae as necrophilous, or Cleridae, Tenebrionidae and Nitidulidae as omnivorous, as well as their appearance on the corpse, is described. Among the Hymenoptera, Formicidae were as the most abundant group, acting as omnivores and not apparently related to any particular decomposition stage. The real cases are discussed using data from the literature and the experimentally obtained results. In every case, the most relevant factors for estimating PMI are briefly discussed, mentioning, when possible, the relation with the experimental results. We confirm the significance of the experimental results because they seem to be applicable to actual forensic cases, the details of which enlarge our very little knowledge on the subject in the Iberian Peninsula. The importance of regional faunistic studies of the sarcosaprophagous arthropod community, the results of which may be applied to forensic practice, is mentioned.     

Pros and cons in the use of SNPs in forensic kinship investigation: a comparative analysis with STRs

Recent advances in single nucleotide polymorphisms (SNPs) research have raised the possibility that these markers could replace the forensically established short tandem repeats (STRs). In this work, we compare STRs and SNPs applicability for kinship investigation in terms of expected informative content and probability of occurrence of "difficult cases" (when isolated Mendelian incompatibilities between alleged father and child are found). Since SNPs have a much lower mutation rate than STRs, these difficulties were expected to occur less frequently if SNPs were used instead of STRs. The purpose of this paper is to make some simulations allowing the estimation of how often such difficult cases are expected to occur using both types of markers and how serious can be their impact in routine work. Our results demonstrate that a battery based exclusively on SNPs matching the informative power of current STR kits would be prone, if applied to routine paternity investigation, to the occurrence of cases where the statistical evidence would be inconclusive. We infer that the introduction of a SNP based strategy, as a substitute to the now classical STR approach poses statistical problems that must be carefully evaluated.     

STR allelic frequencies for an African population sample (Equatorial Guinea) using AmpFlSTR Identifiler and Powerplex 16 kits

We present allele frequencies and forensic parameters for 17 STRs included in the AmpFlSTR Identifiler (CSF1PO, D2S1338, D3S1358, D5S818, D7S820, D8S1179, D13S317, D16S539, D18S51, D19S433, D21S11, FGA, TH01, TPO and VWA) and Powerplex 16 System (CSF1PO, D3S1358, D5S818, D7S820, D8S1179, D13S317, D16S539, D18S51, D21S11, FGA, Penta D, Penta E, TH01, TPO and VWA) in a sample of 134 unrelated individuals from Equatorial Guinea located in Western Africa, between Cameroon and Gabon. Hardy-Weinberg equilibrium was tested for each locus and the sample was compared with five African databases: Promega's and AB Applied Biosystems African-Americans and samples from Mozambique, from Cabinda (Angola) and Guinea-Bissau.     

Stature estimation from radiographically determined long bone length in a Spanish population sample

The estimation of stature from of a variety of bones is an important aspect of forensic work. In order to obtain reliable results, it is important to have comparative data obtained from the same population group as the skeletal remains. However, lack of up to date information on the population groups of Southern Europe makes the estimation of stature from bones in this area subject to possible error. In this study, the stature of 104 healthy adults from Spain was measured, and an anteroposterior teleradiograph of the right lower and the right upper limb of every subject in the study was made in order to measure the lengths of the femur, tibia, fibula, humerus, cubitus and ulna. Pearson's regression formulae were obtained for both limbs. In males, we found the femur to be the most accurate predictor of stature (R = 0.851), whereas in females best results were obtained with the tibia (R = 0.876).     

Allele frequencies of 15 STR loci in the population of the city of Quito, Ecuador

POPULATION: Quito City population (Ecuador, South America, n = 116-207).     

Chemical, physical and mineralogical characterization of soils from the Curitiba Metropolitan Region for forensic purpose

The objective of this paper is to propose a soil characterization methodology for forensic use, based on physical (textural and spectroscopic analyses), chemical (extractions with hydrofluoric acid, ammonium oxalate, sodium dithionite-citrate-bicarbonate and NaOH solution) and mineralogical (thermal analyses and X-ray diffraction) analyses. The study was carried out in the State of Paraná, Brazil, in three neighborhoods of Curitiba city and in two cities within the Curitiba Metropolitan Region. In order to verify the similarity between samples, four composite samples (repetitions) were prepared in each of the five studied sites. It was obtained a great number of quantitative variables (56) from a reduced amount of soil sample (1g). The variables selected from the chemical extractions (16) were more precise in grouping similar samples (same horizon and sampling site) as well as in separating samples collected in different horizons or sites. Seven distinct groups were formed, each with high intragroup similarity, but the unexpected dispersion of two samples (from a total of 40 samples) reduced the distinction of three other studied groups. The placement of the two samples in a different group and the higher dispersion (24 samples) for samples collected in the city of Curitiba are due to the great pedological homogeneity of this area (physical-chemical horizon characteristics, soil color and parent material). The methodology used in this work (analytical method and data treatment) presents high potential for forensic studies and can be easily validated for other areas.     

Sacral fusion as an aid in age estimation

The degree of fusion at the anterior aspect of the sacral vertebrae has been scored in 242 male and female skeletons from the Lisbon documented collection, ranging from 16 to 59 years old in age. Statistical tests indicate a sex difference towards earlier fusion in young females compared with young males, as well as a clear association between degree of fusion and age. Similar results have been found by other authors in documented skeletal samples from Coimbra and Sassari, and the recommendations stated by these authors regarding age estimation have been positively tested in the Lisbon collection. Although more research from geographically diverse samples is required, a general picture of the pattern of sacral fusion and its associations with age and sex is emerging. We also provide a practical example of the usefulness of the sacrum for age estimation in a forensic setting, a mass grave from the Spanish Civil War. It is concluded that the scoring of the degree of fusion of the sacral vertebrae, specially of S(1-2), can be a simple tool for assigning skeletons to broad age groups, and it should be implemented as another resource for age estimation in the study of human skeletal remains.