The effect of linkage on the calculation of DNA match probabilities for siblings and half siblings

The loci in many forensic multiplexes are often selected to avoid linked loci. However as the multiplices used increase in the number of loci represented instances are occurring of loci that are loosely linked. As yet little attention has been paid to the likely consequence of this. We begin the process of developing formulae to give the match probability at two linked loci for full and half siblings. The methodology proceeds from the previously published joint IBD states for two linked loci [B.K. Suarez, J. Rice, T. Reich, The generalized sib pair IBD distribution: its use in the detection of linkage, Ann. Hum. Genet. Lond. 42 (1978) 87; J.K. Haseman, R.C. Elston, The investigation of linkage between a quantitative trait and a marker locus, Behav. Genet. 2 (1972) 3–19]. Our formulation has the drawback of assuming linkage equilibrium. This assumption may be tenable as a first order approximation. We hope to stimulate work on developing better treatments.     

A discussion of the merits of random man not excluded and likelihood ratios

DNA mixture interpretation is undertaken either by calculating a LR or an exclusion probability (RMNE or its complement CPI). Debate exists as to which has the greater claim. The merits and drawbacks of the two approaches are discussed. We conclude that the two matters that appear to have real force are: (1) LRs are more difficult to present in court and (2) the RMNE statistic wastes information that should be utilised.     

Use of DNA profiles for investigation using a simulated national DNA database: Part II. Statistical and ethical considerations on familial searching

Familial searching consists of searching for a full profile left at a crime scene in a National DNA Database (NDNAD). In this paper we are interested in the circumstance where no full match is returned, but a partial match is found between a database member's profile and the crime stain. Because close relatives share more of their DNA than unrelated persons, this partial match may indicate that the crime stain was left by a close relative of the person with whom the partial match was found. This approach has successfully solved important crimes in the UK and the USA. In a previous paper, a model, which takes into account substructure and siblings, was used to simulate a NDNAD [1]. In this paper, we have used this model to test the usefulness of familial searching and offer guidelines for pre-assessment of the cases based on the likelihood ratio. Siblings of “persons” present in the simulated Swiss NDNAD were created. These profiles (N = 10,000) were used as traces and were then compared to the whole database (N = 100,000). The statistical results obtained show that the technique has great potential confirming the findings of previous studies. However, effectiveness of the technique is only one part of the story. Familial searching has juridical and ethical aspects that should not be ignored. In Switzerland for example, there are no specific guidelines to the legality or otherwise of familial searching. This article both presents statistical results, and addresses criminological and civil liberties aspects to take into account risks and benefits of familial searching.     

The development of visual and chemical methods for predicting the likelihood of obtaining a DNA profile from degraded bone samples

Gross morphology, histology and nitrogen content were examined in bone samples from individuals that had been buried for approximately 12 years in Kuwait and Iraq. The results indicate that the gross morphology and histology are useful indicators of DNA survival. Nitrogen content did not show a significant correlation with DNA preservation.     

The analysis of biological samples from crime scene for a future human DNA profile confrontation. Effects of presumptive test reagents on the ability to obtain STR profiles for human identification

Because of the increase of evidence of blood stains, that have been washed or cleaned in an attempt to mask the analysis of DNA profiles, there is also an increase in the use of presumptive tests on samples sent to laboratories. Some of the presumptive tests, used to identify blood and semen stains, could potentially affect the recovery of high molecular weight DNA from the samples, or extinguish them, especially those already present in small quantities. After the presumptive tests, often these samples are discarded. This study aimed to examine the possibility of obtaining a DNA profile from samples submitted for presumptive testing and cleaned with bleaches with and without chlorine. Two different protocols were conducted: (a) A unique sample of human blood in natura (5 μL), already typed through the DNA techniques with the genetic profile previously known (control), was distributed onto cotton fabrics and dried at room temperature. Four samples of fabric were macerated in saline solution and Coombs serum and then stored for three months (room temperature and freezer −20 °C). (b) Another sample of human blood, type A, in natura, already typed through the techniques of DNA (control) was used. Aliquots of 200 μL were distributed in: cotton, denim and synthetic fabric. The samples were dried at room temperature for 24 h. The blood stains in those fabrics (cotton, denim and synthetic) were then divided into three groups: unwashed, cleaned with chlorine bleach and cleaned with chlorine bleach and soap powder. The samples were again dried at room temperature for 24 h, before the use of luminol. The DNA were extracted with Chelex 100 and amplified with the Identifiler Kit (Applied Biosystems). The blood stains exposed to saline and Coombs serum had DNA profiles consistent with untreated samples (controls). This result shows that the experts should keep and store the samples treated with saline and Coombs serum for future DNA confrontation when necessary. Also discussed in this paper the pattern of blood stains after washing with bleaching solutions, as well as the quantity of DNA obtained from these samples.